Paint Calculator

How many gallons of paint to buy for a room or a wall: the wall area minus doors and windows, times the coats, rounded to whole gallons and quarts — with ceiling paint, primer, the cost at your prices and what is left over.

Measure by Room size Wall area

Length

Use decimals — 10 ft 6 in is 10.5.

Width

Wall height

Floor to ceiling.

Doors

20 sq ft each.

Windows

15 sq ft each. Count a patio slider as two doors.

1 coat 2 coats 3 coats

Coverage per coat

sq ft/gal

On the can's label. About 350 for smooth painted walls, 250 for textured, porous or unpainted ones.

Paint the ceiling too

Add a primer coat

New drywall, bare wood, patches, stains or a big color change.

Price per gallon (optional)

Price per quart (optional)

Gallons of wall paint to buy

2 gallons

1.91 gallons needed (7.2 L): 334 sq ft × 2 coats at 350 sq ft per gallon

Paintable wall area

334 sq ft

384 sq ft of wall minus 50 for 1 door and 2 windows

Left in the cans

Wall paint left over

0.09 gal

Enough to touch up about 32 sq ft in one coat

Quarts are bought only for the last half gallon, because three quarts usually cost more than one gallon. Enter both prices to get the cheapest mix at your store.

Same walls, other coverage

Sq ft per gallon	Gallons needed	Buy	Left over, gal
250	2.68	3 gallons	0.32
300	2.23	2 gallons + 1 quart	0.02
350	1.91	2 gallons	0.09
400	1.67	2 gallons	0.33
450	1.49	1 gallon + 2 quarts	0.01

The same 334 sq ft × 2 coats, bought by the same rule as the cards. Data sheets print 250–450 sq ft per gallon; textured, porous or unpainted walls sit at the low end. A highlighted row matches the cards above.

Coverage the makers print

Product	Type	Sq ft per gallon	Coats
Sherwin-Williams ProMar 200 Zero VOC	Interior paint, flat	350–400	2, over 1 coat of primer
Behr Premium Plus Interior	Interior paint, flat	250–400	More for some colors
Benjamin Moore Regal Select	Interior paint, matte	400–450	1 or 2
Valspar 2000 Interior Latex	Interior paint, flat to semi-gloss	350–450	2
Sherwin-Williams ProMar 200 Zero VOC Primer	Interior primer	400	1
Behr Drywall Plus Primer & Sealer	Drywall primer-sealer	250–400	Not stated
Any primer (Sherwin-Williams FAQ)	Primer	200–300	Not stated

Sherwin-Williams prints its coverage for a 4-mil wet film. Valspar: surface conditions and application technique change coverage. Behr: porous, rough, textured or unpainted surfaces take more paint.

How this is calculated

Walls: 2 × (12 ft + 12 ft) × 8 ft = 384 sq ft.

Walls: 384 sq ft, as entered.

Doors and windows: 1 × 20 + 2 × 15 = 50 sq ft, leaving 334 sq ft to paint.

Coats: 334 sq ft × 2 = 668 sq ft to cover.

668 sq ft ÷ 350 sq ft per gallon = 1.91 gallons (7.2 L), rounded up to the hundredth.

668 sq ft ÷ 87.5 sq ft per quart = 7.64, rounded up to 8 quarts.

8 quarts = 2 gallons; buy 2 gallons.

Left over: 2.00 minus 1.91 = 0.09 gal, or 32 sq ft of touch-up at 350 sq ft per gallon.

Ceiling: 12 ft × 12 ft = 144 sq ft; × 2 ÷ 350 = 0.83 gallons, so buy 1 gallon.

Primer: 334 sq ft × 1 coat ÷ 250 = 1.34 gallons, so buy 1 gallon + 2 quarts.

Coverage is per coat: two coats double the paint, not the area.

Gallons needed are rounded up to the hundredth and paint left over down, so the two add up to the cans bought; the cans are rounded up once, to the quart.

Coverage: Sherwin-Williams, Behr, Benjamin Moore and Valspar product data. Door 20 sq ft and window 15 sq ft: Behr. Quart against gallon price: Benjamin Moore. Each is listed under the calculator.

Updated: October 6, 2026

Paint calculator. How many gallons of paint a room needs, and the cans to buy.

This paint calculator works out how many gallons of paint your walls take from the room's length, width and height, minus doors and windows, times the coats. It rounds the answer up to whole gallons and quarts, puts ceiling paint and primer in cans of their own, and shows how much wall the leftover paint will touch up.

How much paint a room takes, from wall area to cans

The paint a room needs is its wall area, minus doors and windows, times the number of coats, divided by the coverage printed on the can. A 12 × 12 ft bedroom with 8 ft walls, one door and two windows has 384 sq ft of wall; taking off 50 sq ft for the openings leaves 334 sq ft. Two coats make 668 sq ft to cover, and at 350 sq ft per gallon that is 1.91 gallons of paint. You buy 2 gallons, and 0.09 gal stays in the cans.

Coverage is the figure to check on the label first, because the data sheets spread it wide. Sherwin-Williams prints 350–400 sq ft per gallon for ProMar 200 Zero VOC flat at a 4-mil wet film, Behr 250–400 for Premium Plus Interior flat, Benjamin Moore 400–450 for Regal Select matte and Valspar 350–450 for Valspar 2000. The calculator starts at 350, the low end of the Sherwin-Williams and Valspar ranges, and the hint on "Coverage per coat" suggests 250 for textured, porous or unpainted walls, which Behr says take more paint. In the same bedroom, 250 sq ft per gallon means buying 3 gallons and 450 means 1 gallon + 2 quarts; the "Same walls, other coverage" table under the cards lists the steps in between.

Each door counts as 20 sq ft and each window as 15 sq ft, the averages Behr gives in its guide to exterior paint. The hint under Windows counts a patio slider as two doors. In October 2026 the Sherwin-Williams, Behr and Benjamin Moore calculators subtracted 21 sq ft per door and 15, 20 and 12 sq ft per window, so the same room could start a few square feet apart before any paint is involved.

Paint is sold by the quart and the gallon, so the calculator counts the job in quarts, each covering a quarter of the gallon figure (87.5 sq ft at 350), rounds up once and groups the quarts into gallons. A remainder of one or two quarts stays as quarts, and a remainder of three is bought as one more gallon. Benjamin Moore's list prices in October 2026 put a quart of Regal Select matte at about 41% of the gallon price, which makes two quarts cheaper than a gallon and three more expensive. Type a price per gallon and a price per quart and the calculator uses your store's prices instead: the last quarts are bought as a gallon whenever they would cost as much as one or more, and the buy card shows the total.

Ceiling paint and primer get cards and cans of their own. The ceiling is length × width at the same coats and coverage as the walls: in the 12 × 12 bedroom, 144 sq ft × 2 coats is 0.83 gallons, so 1 gallon. Primer is one coat over the walls, plus the ceiling when "Paint the ceiling too" is on, at its own coverage of 250 sq ft per gallon unless you change it: 478 sq ft of wall and ceiling take 1.92 gallons, so 2 gallons. The two price fields cost the wall paint only.

The "Wall paint left over" card shows what the rounding leaves in the cans, with a can drawing filled to that level, and how much wall it will touch up in one coat: 0.09 gal and about 32 sq ft in the bedroom above. The folded "How this is calculated" section below the table repeats each step with your numbers.

Gallons of paint by room size (8 ft walls, 1 door, 2 windows, 2 coats at 350 sq ft per gallon)

Room	Wall area to paint	Gallons needed	Buy	Left over
10 × 10 ft	270 sq ft	1.55	2 gallons	0.45 gal
10 × 12 ft	302 sq ft	1.73	2 gallons	0.27 gal
12 × 12 ft	334 sq ft	1.91	2 gallons	0.09 gal
12 × 14 ft	366 sq ft	2.10	2 gallons + 1 quart	0.15 gal
14 × 16 ft	430 sq ft	2.46	2 gallons + 2 quarts	0.04 gal
15 × 20 ft	510 sq ft	2.92	3 gallons	0.08 gal
20 × 20 ft	590 sq ft	3.38	3 gallons + 2 quarts	0.12 gal

One bedroom, from tape measure to shopping list

Sam has hung new drywall in a 12 × 12 ft bedroom with 8 ft walls, one door and two windows. The walls and the ceiling get two coats, the new board needs primer, and the store sells the wall paint at $45 a gallon and $18 a quart.

1. Sam measures two walls along the floor and the height from floor to ceiling, leaves "Measure by" on Room size and checks Length, Width and Wall height: 12, 12 and 8, the values the calculator opens with. A wall of 10 ft 6 in would go in as 10.5.

2. Doors and Windows already read 1 and 2. The "Paintable wall area" card shows 334 sq ft: 384 sq ft of wall minus 50 for 1 door and 2 windows.

3. The label on the wall paint prints 350–400 sq ft per gallon. Sam keeps 2 coats and leaves "Coverage per coat" at 350, planning on the low end of the label. The buy card reads 2 gallons, with 1.91 gallons needed (7.2 L).

4. Switching on "Paint the ceiling too" adds the "Ceiling paint to buy" card: 144 sq ft × 2 coats, 0.83 gallons needed, so 1 gallon.

5. New drywall is the first case the hint on "Add a primer coat" names, so Sam switches it on and leaves "Primer coverage" at 250. The "Primer to buy" card covers 478 sq ft of wall and ceiling in one coat: 1.92 gallons needed, so 2 gallons.

6. Sam types 45 under "Price per gallon (optional)" and 18 under "Price per quart (optional)". The wall paint stays at 2 gallons and the card adds "About $90.00 — 2 gallons at $45.00". The ceiling paint and the primer are priced at the shelf, since the two fields cost the wall paint only.

7. The "Wall paint left over" card reads 0.09 gal, enough to touch up about 32 sq ft in one coat. The shopping list is 2 gallons of wall paint, 1 gallon of ceiling paint and 2 gallons of primer.

The page address carries every setting that differs from the starting values, so a texted or bookmarked link reopens the room with the same switches and prices.

The formula for gallons of paint, and how the cans are counted

G = \frac{\left[\,2(L + W)\,H - 20\,n_d - 15\,n_w\,\right] \times C}{S}

$G$ = Gallons of wall paint needed, shown rounded up to the hundredth
$L$ = Room length in feet; 10 ft 6 in is 10.5
$W$ = Room width in feet
$H$ = Wall height from floor to ceiling, in feet
$n_d$ = Number of doors, 20 sq ft each
$n_w$ = Number of windows, 15 sq ft each
$C$ = Number of coats: 1, 2 or 3
$S$ = Coverage per coat from the can's label, in sq ft per gallon (350 to start)

The walls of a rectangular room are its perimeter times its height. Take the doors and windows off that area, multiply by the coats and divide by the coverage. With Wall area selected, the figure you type takes the place of 2(L + W)H and the rest of the formula is the same.

On the 12 × 12 bedroom with 8 ft walls: 2 × (12 + 12) × 8 = 384 sq ft of wall. 1 × 20 + 2 × 15 = 50 sq ft of openings, leaving 334 sq ft. 334 × 2 coats = 668 sq ft to cover, and 668 ÷ 350 = 1.91 gallons, or 7.2 L at 3.785 412 L per US gallon (NIST SP 811).

The purchase is counted in quarts, each covering a quarter of the gallon figure:

Q = \left\lceil \frac{A \times C}{S / 4} \right\rceil

Here A is the paintable area. 668 ÷ 87.5 = 7.64, rounded up to 8 quarts, which makes 2 gallons. Whole gallons are taken out first; a remainder of one or two quarts is bought as quarts and a remainder of three as another gallon. With both prices entered, the last quarts are bought as a gallon whenever they would cost as much as one or more.

The gallons needed are rounded up to the hundredth and the paint left over is the cans bought minus the gallons needed, so the two add up: 2.00 − 1.91 = 0.09 gal. The touch-up area on the leftover card is what the cans cover in one coat minus the area the coats take, rounded down to the square foot: two gallons cover 700 sq ft in one coat, 32 sq ft more than the 668 the walls take.

The ceiling is L × W at the same coats and coverage: 144 × 2 ÷ 350 = 0.83 gallons. Primer is one coat over the walls, plus the ceiling when it is switched on, at the primer's coverage: 478 ÷ 250 = 1.92 gallons. Each one is rounded into its own cans by the same quart rule.

Five paint jobs worked through

Textured walls at a store with cheap quarts: 2 gallons + 3 quarts

A 12 × 12 ft room with 8 ft walls, one door, two windows and a knockdown texture. The paint's label prints 250–400 sq ft per gallon, so "Coverage per coat" goes to 250; the store charges $45 a gallon and $14 a quart.

Two coats over 334 sq ft is 668 sq ft, and 668 ÷ 250 is 2.68 gallons, or 11 quarts once rounded up. Without prices, 11 quarts is 2 gallons and 3 quarts, and the three quarts are bought as a gallon: 3 gallons, with 0.32 gal left over.

With both prices typed in, the three quarts cost $42 and the extra gallon $45, so the card shows 2 gallons + 3 quarts, about $132.00 in all, and 0.07 gal left over, enough to touch up about 19 sq ft. At $18 a quart the same three quarts would cost $54 and the card goes back to 3 gallons.

One accent wall: 2 quarts for one coat, 1 gallon for two

An accent wall 12 ft wide and 8 ft high is 96 sq ft. Set "Measure by" to Wall area, type 96 and set Doors and Windows to 0.

At 350 sq ft per gallon, one coat takes 0.28 gallons and the card says 2 quarts, with 0.22 gal left, about 79 sq ft of touch-up. Two coats take 0.55 gallons, which is 3 quarts, so the card says 1 gallon and 0.45 gal stays in the can, enough for about 158 sq ft more. Three coats take 0.83 gallons, still 1 gallon.

Sherwin-Williams says a quart covers 100 sq ft, enough for an accent wall, which matches one coat at 400 sq ft per gallon. At that coverage the same wall in two coats takes 0.48 gallons, and 2 quarts cover it with 0.02 gal to spare.

A house exterior: 10 gallons + 2 quarts, or two 5-gallon pails + 2 quarts

Behr's guide to exterior paint starts from the perimeter: multiply the perimeter of the house by the wall height, then add width × height ÷ 2 for each gable. A 40 × 30 ft house with 13 ft from the ground to the roofline has 140 ft of perimeter and 1,820 sq ft of wall; two gables 30 ft wide and 6 ft high add 90 sq ft each, for 2,000 sq ft.

Under Wall area, type 2000 and count 2 doors and 10 windows: 190 sq ft come off, leaving 1,810 sq ft. Two coats at 350 sq ft per gallon take 10.35 gallons (39.2 L). The card says 10 gallons + 2 quarts and adds a note: "The same paint in 5-gallon pails: 2 pails + 2 quarts". The leftover is 0.15 gal, about 55 sq ft of touch-up.

Exterior paints print their own coverage, so type the figure from the exterior can before buying. Behr sells its paints in quarts for small areas and in five-gallon pails for very large ones.

A deep color over a light one: three coats, or primer and two

The 12 × 12 bedroom is going from off-white to a dark green.

Three coats: 334 sq ft × 3 = 1,002 sq ft, which is 2.87 gallons at 350 sq ft per gallon. The card says 3 gallons and 0.13 gal is left, about 48 sq ft of touch-up.

Primer and two coats: the walls take 2 gallons of paint, and switching on "Add a primer coat" adds a "Primer to buy" card for 334 sq ft of wall at 250 sq ft per gallon, 1.34 gallons, bought as 1 gallon + 2 quarts. Sherwin-Williams' ProMar 200 data sheet says a coat of primer improves hiding on a drastic color change, and Behr sells its Drywall Plus Primer & Sealer as tintable for one. The paint store can tint the primer toward the new color before the first topcoat goes on.

Whole gallons against gallons and quarts at 300 sq ft per gallon

The same bedroom with a paint whose label prints 300 sq ft per gallon, at $45 a gallon and $18 a quart. The walls take 2.23 gallons, which is 9 quarts.

Rounded up to whole gallons, that is 3 gallons and 0.77 gal left over, $135 at the shelf price. The card says 2 gallons + 1 quart instead, about $108.00 at those prices, with 0.02 gal left over, enough for about 7 sq ft of touch-up.

The quart saves $27 and leaves less paint to store. If the walls take knocks and you want more on the shelf, the third gallon is a choice to make on purpose, with its cost in view.

Mistakes that lead to the wrong number of cans

Measuring the floor instead of the walls. A 12 × 12 ft room has 144 sq ft of floor and 384 sq ft of wall at 8 ft. The coverage on the label is for the surface you roll, so the walls are the perimeter times the height; the floor area is the ceiling's figure.
Buying for one coat when you plan two. Coverage is per coat. The walls of the 12 × 12 bedroom take 0.96 gallons for one coat and 1.91 for two, so a single gallon runs dry about 16 sq ft into the second coat.
Rounding up to whole gallons. A 12 × 14 ft room with 8 ft walls takes 2.10 gallons for two coats. Rounded to whole gallons that is 3 gallons and 0.90 gal spare; bought as 2 gallons + 1 quart it leaves 0.15 gal.
Buying three quarts instead of a gallon. At Benjamin Moore's October 2026 list prices a quart cost about 41% of a gallon, so three quarts cost more than the gallon while holding three-quarters of the paint. The calculator only keeps three quarts when your own prices make them cheaper.
Planning rough walls at the top of the label's range. Textured, porous or unpainted walls belong at the low end of a label range such as 250–400 sq ft per gallon, because Behr says those surfaces take more paint. For the 12 × 12 bedroom that is 2 gallons at 400 and 3 gallons at 250, so plan on the low end for texture or bare, unpainted board.
Spot-priming new or patched drywall. Sherwin-Williams' ProMar 200 primer data sheet calls for priming the entire surface rather than spot priming. Switch on "Add a primer coat" so the primer card counts every wall, and the ceiling too when it is on.

What the paint calculator leaves out

The calculator works on flat, rectangular walls and a flat ceiling. Trim, baseboards, doors and cabinets are not part of the estimate, so a door you also plan to paint is still subtracted as 20 sq ft of wall and needs its own paint. Gables and sloped or L-shaped walls need their square feet worked out first, by hand or in the area calculator, and typed under Wall area.

Coverage is one number per run. A room with three smooth walls and one textured wall can be run twice under Wall area, once per surface, with each door and window counted only in the run for its own wall and the cans from the two runs added together. The ceiling takes the walls' coverage and coats; if your ceiling paint prints a different coverage, run the ceiling under Wall area with its own figure and Doors and Windows set to 0.

There is no waste percentage field. Rounding up to whole quarts already leaves paint over, and the leftover card shows how much. For a wider margin, read the row with the lower coverage in "Same walls, other coverage".

The prices cost the wall paint only, with no labor or sales tax. Measurements go in feet and square feet; the buy card adds liters, and the volume converter turns gallons into pints or fluid ounces.

Paint calculator questions

How many gallons of paint do I need for a 12x12 room?

Two gallons for two coats on the walls. A 12 × 12 ft room with 8 ft walls, one door and two windows has 334 sq ft to paint; two coats at 350 sq ft per gallon take 1.91 gallons, leaving 0.09 gal in the cans. Painting the ceiling as well adds 1 gallon.

How do I calculate how much paint I need for a room?

Add the lengths of the walls and multiply by the height from floor to ceiling. Take off 20 sq ft for each door and 15 for each window, multiply by the number of coats and divide by the coverage on the can. For a 12 × 12 room with 8 ft walls, one door and two windows: 384 − 50 = 334 sq ft, times 2 coats is 668, divided by 350 is 1.91 gallons. Then round up to cans you can buy, which here is 2 gallons.

How many square feet does a gallon of paint cover?

Sherwin-Williams' paint calculator FAQ gives 350–400 sq ft per gallon, and the interior paints in the "Coverage the makers print" fold under this calculator print between 250 and 450 sq ft per gallon. Behr says porous, rough, textured or unpainted surfaces take more paint, so those walls sit at the low end. The calculator starts at 350, and its hint suggests 250 for those surfaces.

How much does a quart of paint cover?

A quarter of what a gallon covers: 87.5 sq ft per coat at 350 sq ft per gallon, and 100 sq ft at 400, the figure Sherwin-Williams uses. One coat on a 12 × 8 ft accent wall (96 sq ft) at 350 takes 2 quarts.

Do I need twice as much paint for two coats?

Yes. Coverage is per coat, so two coats double the paint while the wall area stays the same. The walls of a 12 × 12 bedroom take 0.96 gallons for one coat, 1.91 for two and 2.87 for three.

How many coats of paint do I need?

Three of the four paints in the "Coverage the makers print" fold mention two coats: Sherwin-Williams ProMar 200 Zero VOC calls for 2 coats over 1 coat of primer on drywall, Valspar 2000 recommends 2 and Benjamin Moore Regal Select says 1 or 2. Behr notes that certain colors may require additional coats for complete hide. The calculator starts at 2 coats; choose 3 for a deep color over a light one, or add a primer coat, which Sherwin-Williams says improves hiding on a drastic color change.

How much primer do I need for new drywall?

One coat over every surface you prime, at the primer's own coverage. The calculator starts at 250 sq ft per gallon, inside the 200–300 that Sherwin-Williams gives for a gallon of primer and at the low end of the 250–400 Behr prints for Drywall Plus Primer & Sealer. The walls of a 12 × 12 bedroom (334 sq ft) take 1.34 gallons, bought as 1 gallon + 2 quarts; walls and ceiling together (478 sq ft) take 1.92 gallons, so 2 gallons.

How much paint do I need for a ceiling?

The ceiling's area is length × width, painted at the coats and coverage you set for the walls. A 12 × 12 ceiling is 144 sq ft; two coats at 350 sq ft per gallon take 0.83 gallons, so 1 gallon. With "Paint the ceiling too" switched on, it gets its own card and cans, apart from the wall color.

Is it cheaper to buy quarts or a gallon of paint?

For one or two quarts, the quarts; for three, the gallon. At Benjamin Moore's list prices in October 2026, a quart of Regal Select matte cost about 41% of a gallon of the same paint, so two quarts cost less than a gallon and three cost more. Type both of your store's prices and the calculator compares them for your cans.

How much paint do I need for one accent wall?

For a 12 × 8 ft wall (96 sq ft) at 350 sq ft per gallon, 2 quarts for one coat and 1 gallon for two, because two coats take 0.55 gallons, which is 3 quarts. Pick Wall area, type width × height and set doors and windows to 0.

How many gallons of paint do I need for 1,000 square feet?

For 1,000 sq ft of wall at 350 sq ft per gallon, with doors and windows set to 0, one coat takes 2.86 gallons, bought as 3 gallons, and two coats take 5.72 gallons, bought as 6 gallons. A house sold as 1,000 sq ft is measured on the floor; its walls are the perimeter times the height, and that is the figure to enter under Wall area.

Why does the Behr or Sherwin-Williams calculator give me a different amount?

Each one assumes something different. Run on a 12 × 12 room with 8 ft walls, one door and two windows in October 2026, Sherwin-Williams' quick calculator answered for one coat at 400 sq ft per gallon (0.9 gallons), Behr's has no wall-height field and assumes 9 ft walls and one coat (1 gallon + 1 quart), and Benjamin Moore's assumes two coats at 350 (2 gallons). All three count a door as 21 sq ft, and a window as 15, 20 and 12 sq ft. Sherwin-Williams' answer, doubled for two coats and rounded up to the gallon as it recommends, also comes to 2 gallons. Here wall height, coats and coverage are yours to set: at 9 ft the same room takes 2.19 gallons, bought as 2 gallons + 1 quart.

How much extra paint should I buy for touch-ups?

Look at the leftover card before adding any. Rounding up to whole quarts already leaves paint in the cans: 0.09 gal in the 12 × 12 bedroom, enough to touch up about 32 sq ft in one coat, and 0.45 gal in a 10 × 10 room. If the leftover card shows only a few square feet and the walls take knocks, one more quart of the same paint adds 87.5 sq ft of touch-up at 350 sq ft per gallon.

What should I do with the leftover paint?

Keep it sealed for touch-ups. Benjamin Moore's storage guide says to reseal the can, keep it between 60 and 80 °F out of direct sunlight, and label it with the brand, color, product, sheen and the room it went on; it says most opened paint has a shelf life of two years. Latex paint you will not use can go to a paint drop-off site: PaintCare, a paint stewardship organization with drop-off sites in the states where it runs a program, sends most of the leftover latex paint it collects to recyclers.

Can I use the paint calculator for exterior walls?

Yes, through Wall area. Behr's guide works the area out as the perimeter of the house times the wall height, plus width × height ÷ 2 for each gable. A 2,000 sq ft exterior with 2 doors and 10 windows takes 10.35 gallons for two coats at 350 sq ft per gallon: 10 gallons + 2 quarts, which the card also gives as 2 five-gallon pails + 2 quarts. Type the coverage printed on the exterior paint before you buy.

Is the paint calculator free, and can I send my room to someone?

Yes, it is free and has no sign-up. The page address carries your room once you change a value, so the link reopens the same walls, coats, coverage, switches and prices on another phone or computer.

How close is the estimate to the paint my walls will take?

It is as close as the coverage you type. The arithmetic is exact and the cans are rounded up, so the gap comes from the label figure and your walls: the 12 × 12 bedroom takes 2.68 gallons at 250 sq ft per gallon and 1.49 at 450. The "Same walls, other coverage" table under the cards shows what each step of that range would have you buy, so you can see whether the low end of your label changes the purchase.

Sources & References

Content verified by the Smart Calculators Team