Construction

Building and construction calculation tools

Area Calculator

Area of any plane figure — rectangle, triangle, circle, sector, trapezoid, polygon and more — drawn to scale with your dimensions on it.

Work out how many bags of concrete and how many cubic yards a slab, round pad, footing, wall, column, post hole or set of stairs needs — with an editable waste allowance, real published bag yields and a stated bags-versus-ready-mix threshold.

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Construction Calculators

Estimating tools for the moment before you buy materials: how much a pour, a fill or a coat actually takes, and what that comes to in bags, yards or tons.

The collection starts with concrete and is growing. Each tool works from the figures the manufacturers publish rather than from a rule of thumb, so the number you carry to the store is one you can check.

Concrete

The concrete calculator turns the dimensions of a pour into how many bags to buy and how many cubic yards to order, across seven shapes: slabs, round pads, footings, walls, columns, post holes and stairs. Bag counts come from the yields QUIKRETE and Sakrete print on their data sheets, not from dividing a weight by a density — which is where the largest of the competing calculators lands about 12% high.

It also does the two things a store aisle actually asks for: a waste allowance you can edit, set to 10% by default, and a stated threshold for when a ready-mix truck beats bags.

Estimating Before You Buy

Materials are sold in whole units, so an estimate that ends in a fraction is not yet an answer. These calculators round up to what you can put in a trolley, show the plan volume beside the ordered volume so you can see exactly what the allowance added, and name the source of every published figure they use.

Is there a construction estimate you keep doing by hand? We are still adding tools to this category, and that is where the list comes from.

Frequently Asked Questions

How many bags of concrete do I need?

It depends on the volume, not the area. Measure the pour, and the concrete calculator divides that volume by the yield printed on the bag — 0.60 cu ft for an 80 lb bag, 0.45 for a 60 lb — then rounds up, because you cannot buy part of a bag. A 10 × 10 ft slab 4 in thick takes 62 bags of 80 lb with a 10% allowance included.

Should I buy bags or order a ready-mix truck?

Under one cubic yard, buy bags: a truck's minimum load is more concrete than the job needs. Above four cubic yards, order the truck — that is 180 bags of 80 lb, 14,400 lb of dry mix to carry and mix, and NRMCA advises against loads smaller than four yards. In between, ask for a quote, because suppliers commonly add a fee below their minimum.

Are these calculators free to use?

Yes, every calculator here is free and needs no sign-up. Open the one you need, enter your measurements, and the results update as you type.