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Temperature Converter

Convert between Celsius, Fahrenheit, Kelvin, Rankine, and Réaumur temperatures. Handles non-multiplicative scales correctly using the SI offset definition (0 °C = 273.15 K exactly, 13th CGPM 1967).

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°F

Result

-17.2222 °C

1 °F≈ -17.222222 °C

UnitValue
Kelvin (K)255.928
Celsius (°C)-17.2222
Fahrenheit (°F)1
Rankine (°R)460.67
Réaumur (°Ré)-13.7778
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Temperature converter. Convert Celsius, Fahrenheit, Kelvin, Rankine and Réaumur.

A temperature converter switches a value between Celsius, Fahrenheit, Kelvin, Rankine and Réaumur. It applies the offset each scale needs — the +32 for Fahrenheit, the 273.15 for Kelvin — so it accounts for each scale's zero point, not just its degree size.

What Is a Temperature Converter?

0 °C is 32 °F, 100 °C is 212 °F, and at −40 the two scales finally meet — the one temperature that reads the same number in Celsius and Fahrenheit. Keep those three anchors in your head and most everyday conversions fall into place, but they also expose what makes temperature odd. Length, mass and volume all share a zero: zero meters is zero feet, so a single multiplication does the whole job. Celsius and Fahrenheit do not share a zero — 0 °C sits at 32 °F — so converting between them takes two moves instead of one. First you resize the degree by multiplying by 9/5, then you shift the zero by adding 32. That extra shift is what makes the relationship affine rather than a simple ratio, and it is the reason −40 is special and the reason so many quick mental conversions land 32 degrees off.
Under the hood the tool runs everything through one absolute reference — the kelvin — and each scale carries both a slope (how wide its degree is) and an offset (where its zero sits). Celsius uses the same degree as Kelvin but slides the zero up to freezing water. Fahrenheit shrinks the degree to five-ninths of a Celsius degree and puts its zero lower still. Rankine borrows the Fahrenheit-sized degree but drops the zero all the way to absolute zero. Because Celsius, Kelvin and Réaumur reach the kelvin base through terminating slope factors (×1 for Celsius and Kelvin, ×1.25 for Réaumur) while Fahrenheit and Rankine ride the repeating 5/9 factor, some results come out exact and others are rounded — and the converter marks which is which, so you never have to guess whether a figure is a definition or a decimal that got cut short.
Five scales are covered, and each earns its place. Celsius and Fahrenheit are the everyday pair — weather, thermostats, fevers, oven dials — with most of the world on Celsius and the United States on Fahrenheit. Kelvin is the scientific standard, the SI base unit for temperature, and it never goes negative because its zero is absolute zero, the coldest anything can get. Rankine is the second absolute scale here: the same starting point as Kelvin but built on Fahrenheit-sized degrees, so 0 °R is absolute zero and water freezes at 491.67 °R. It still shows up in US aerospace, HVAC and power-plant work, where the surrounding math is already in Fahrenheit. Réaumur is the historical outlier — water freezes at 0 °Ré and boils at 80 °Ré, which makes one Réaumur degree equal to 1.25 °C. It has almost disappeared, surviving mainly in a handful of Italian and Swiss cheese dairies and in old European recipes and novels — exactly the moments when you want a converter that still speaks it.

How to Use the Temperature Converter

The converter works in three steps:
1. Choose the scale you are starting from in the From menu — Celsius, for example.
2. Choose the scale you want in the To menu — say, Fahrenheit.
3. Type your value. The result appears as you type, and you can click it to copy.
It opens on Fahrenheit to Celsius, the direction most US readers reach for first, and either menu switches to any of the five scales at any time.
To run the same math by hand, the Celsius-to-Fahrenheit case is the one worth memorizing: multiply by 9/5 (that is 1.8), then add 32, so 20 °C becomes 20 × 1.8 + 32 = 68 °F. Going the other way, undo the steps in reverse — subtract 32 first, then multiply by 5/9 — so (212 − 32) × 5/9 = 100 °C. Kelvin needs no factor at all: add 273.15 to a Celsius reading and you are done, which is why 0 °C is 273.15 K. Because Fahrenheit and Rankine both run on the repeating 5/9 factor, the converter labels those results approximate and marks the offset-clean Celsius, Kelvin and Réaumur pairs exact, so you always know which digits are rounded.
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Temperature Conversion Formulas

∘F=∘C×95+32{}^{\circ}F = {}^{\circ}C \times \frac{9}{5} + 32
  • ∘C{}^{\circ}C = Temperature in Celsius — the value you start from
  • ∘F{}^{\circ}F = Temperature in Fahrenheit — the result
  • 95\frac{9}{5} = The slope, or 1.8 — each Celsius degree spans 1.8 Fahrenheit degrees
  • 3232 = The offset — added because 0 °C sits at 32 °F, not at 0 °F
Three formulas cover every everyday conversion. To go from Celsius to Fahrenheit, multiply by 9/5 and add 32: °F = °C × 9/5 + 32. To reverse it, undo those steps in order — subtract 32 first, then multiply by 5/9: °C = (°F − 32) × 5/9. Kelvin skips the multiplication and only shifts the zero: K = °C + 273.15.
What ties them together is the offset. A pure unit conversion — kilograms to pounds, say — is a straight multiplication because both units agree that zero means "nothing." Temperature scales disagree about where zero belongs: Celsius pins it to freezing water, Fahrenheit to a colder reference, Kelvin to absolute zero. So each conversion needs two numbers, a slope to resize the degree and an offset to move the zero — that pairing is what makes temperature affine rather than proportional, and it is why you cannot convert by multiplying alone. Rankine and Réaumur follow the same pattern with their own numbers: Rankine keeps the Fahrenheit-sized degree but starts at absolute zero (°R = °F + 459.67), and Réaumur uses a degree 1.25 times a Celsius degree (°Ré = °C × 4/5).

Common Temperatures in Celsius, Fahrenheit and Kelvin

Reference pointCelsiusFahrenheitKelvin
Celsius = Fahrenheit−40 °C−40 °F233.15 K
Water freezes0 °C32 °F273.15 K
Room temperature20 °C68 °F293.15 K
Body temperature37 °C98.6 °F310.15 K
Water boils (sea level)100 °C212 °F373.15 K
Oven — 350 °F baking176.667 °C350 °F449.817 K
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Worked Temperature Conversions

A mild day: 20 °C to Fahrenheit

A spring afternoon of 20 °C is a comfortable 68 °F. Multiply by 1.8 and add 32: 20 × 1.8 = 36, then 36 + 32 = 68 °F. That +32 is the whole story of why weather feels so different by the numbers — drop it and you would report a chilly 36 °F for the same pleasant day.

Body temperature: 37 °C both ways

The textbook body temperature of 37 °C works out to 98.6 °F: 37 × 1.8 = 66.6, then 66.6 + 32 = 98.6 °F. Reverse it and the steps run backward — a thermometer reading 98.6 °F converts as (98.6 − 32) × 5/9 = 66.6 × 5/9 = 37 °C. Treat 37 °C = 98.6 °F as a reference point, since healthy readings drift a little through the day.

Baking: 350 °F to Celsius

A US recipe calling for 350 °F means 176.667 °C: subtract 32 to get 318, then 318 × 5/9 = 176.667 °C. Most cooks round to the nearest oven mark — around 175 to 180 °C, the setting conventionally labeled gas mark 4. What you must not do is dial a Celsius oven to 350; that would run hot enough to scorch the food.

Absolute zero: 0 K in Celsius and Fahrenheit

Absolute zero, 0 K, is the coldest temperature there is. Kelvin to Celsius only removes the 273.15 offset: 0 − 273.15 = −273.15 °C. Then Celsius to Fahrenheit finishes the job: −273.15 × 1.8 = −491.67, then −491.67 + 32 = −459.67 °F. On the Rankine scale the same point is simply 0 °R, since Rankine, like Kelvin, starts at absolute zero.

A historical recipe: 80 °Ré to Celsius

An old European recipe that says "heat to 80 degrees Réaumur" means boiling water — 100 °C. A Réaumur degree is 1.25 times a Celsius degree, so you multiply by 5/4: 80 × 5/4 = 100 °C, which is 212 °F. The Réaumur scale set water's freezing point at 0 °Ré and its boiling point at 80 °Ré, which is why the numbers on an antique thermometer look so unfamiliar today.

Common Temperature Conversion Mistakes

  • Multiplying by 1.8 but forgetting the +32. This is the number-one Celsius-to-Fahrenheit slip. The × 9/5 step only resizes the degree; you still have to add 32 to move the zero. 20 °C is 68 °F, not 36 °F — leave out the +32 and every answer lands 32 degrees too low.
  • Confusing a temperature change with a temperature. When something warms by 1 °C it warms by 1.8 °F, and that interval uses the 9/5 factor alone — no +32. But 1 °C as a reading is not 1.8 °F. Water freezing (0 °C = 32 °F) and boiling (100 °C = 212 °F) shows both facts at once: 100 Celsius degrees cover the same span as 180 Fahrenheit degrees, so each Celsius degree is 1.8 Fahrenheit degrees wide.
  • Assuming other round numbers line up the way −40 does. −40 °C = −40 °F is the only point where the two scales read the same, because the 9/5 stretch and the 32 shift happen to cancel there. Everywhere else the numbers differ, so do not expect 0, 100 or any other figure to match across scales.
  • Adding 273 instead of 273.15 for Kelvin. Kelvin is Celsius plus 273.15, not a rounded 273. 0 °C is exactly 273.15 K, and dropping the .15 leaves a steady 0.15 K error in every result. Skip the degree symbol too: it is 273.15 K, never 273.15 °K.
  • Reading an oven's Fahrenheit setting as Celsius. A recipe that says 350 °F means 176.667 °C, not 350 °C. Setting a Celsius oven to 350 for a US recipe would run it hot enough to burn the food — always check which scale a temperature is in before you dial it in.
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Temperature Converter — Frequently Asked Questions

How do I convert Celsius to Fahrenheit?

Multiply by 9/5 (which is 1.8) and add 32. So 20 °C × 1.8 + 32 = 68 °F and 100 °C × 1.8 + 32 = 212 °F. The +32 is essential — without it the answer comes out 32 degrees too low.

How do I convert Fahrenheit to Celsius?

Subtract 32 first, then multiply by 5/9. So (98.6 − 32) × 5/9 = 37 °C and (68 − 32) × 5/9 = 20 °C. Subtracting the 32 before you multiply is the step people most often skip.

Is there a quick way to estimate Celsius to Fahrenheit in my head?

Double the Celsius value and add 30. So 20 °C is roughly 20 × 2 + 30 = 70 °F, close to the exact 68 °F. The shortcut is fine for weather because it skips the fussy 1.8, but it drifts a few degrees, so use the full 9/5 × plus 32 when the number has to be right.

Why do the Celsius-to-Fahrenheit formulas add 32?

Because the two scales do not share a zero. Water freezes at 0 °C but at 32 °F, so after you resize the degree with the 9/5 factor you still have to shift the zero up by 32 to line the scales up.

Why does −40 °C equal −40 °F?

Because the two scales cross exactly once. Celsius and Fahrenheit have different degree sizes (1 °C = 1.8 °F) and different zeros (0 °C = 32 °F), and at −40 the 9/5 stretch and the 32 shift cancel out. It is the single temperature both scales report with the same number — everywhere else they differ.

Which is colder, −40 °C or −40 °F?

Neither — they are the same temperature. −40 is the one point where Celsius and Fahrenheit meet, so −40 °C and −40 °F describe an identical degree of cold.

What is 100 °C in Fahrenheit?

100 °C is 212 °F, the boiling point of water at sea level. Water freezes at 0 °C = 32 °F, so the 100-degree Celsius gap between freezing and boiling shows up as a 180-degree gap in Fahrenheit.

What is 20 °C in Fahrenheit?

20 °C is 68 °F, a common indoor room temperature. Multiply by 1.8 to get 36, then add 32 to reach 68 °F.

Is 37 °C a normal body temperature?

37 °C is the classic textbook figure, equal to 98.6 °F. In practice, healthy readings vary from person to person and across the day, so treat 37 °C = 98.6 °F as a reference point rather than a fixed target when you read a thermometer.

What is 350 °F in Celsius for baking?

350 °F is 176.667 °C, the standard US baking temperature. Round it to your oven's nearest mark — about 175 to 180 °C, the setting often labeled gas mark 4. Do not set a Celsius dial to 350 for a US recipe; that is far hotter and would burn most food.

How do I convert Celsius to Kelvin?

Add 273.15. So 0 °C = 273.15 K and 100 °C = 373.15 K. There is no multiplication and no degree symbol on Kelvin — write 273.15 K, not 273.15 °K.

What is absolute zero in Celsius and Fahrenheit?

Absolute zero is 0 K, the lowest temperature there is. That equals −273.15 °C and −459.67 °F. On the Rankine scale it is 0 °R, because Rankine, like Kelvin, starts at absolute zero rather than at water's freezing point.

Why is Kelvin written without a degree symbol?

Since 1967, Kelvin carries no degree symbol: write 100 K, never 100 °K. Celsius, Fahrenheit, Rankine and Réaumur keep the ° because they are scales, while the kelvin is the base unit of temperature itself.

What are the Rankine and Réaumur scales?

Rankine is an absolute scale with Fahrenheit-sized degrees: 0 °R is absolute zero and 491.67 °R is water's freezing point, still used in some US aerospace, HVAC and power-plant engineering. Réaumur sets water freezing at 0 °Ré and boiling at 80 °Ré, so 1 °Ré = 1.25 °C; it survives mainly in old European recipes, a few cheese dairies and nineteenth-century novels.

How accurate is this converter?

The definitions are exact: 0 °C = 273.15 K, 32 °F = 0 °C, and 80 °Ré = 100 °C are all fixed by standard. Conversions through Celsius, Kelvin and Réaumur are exact, while those through Fahrenheit or Rankine use the repeating 5/9 factor — the tool flags which results are exact and which are rounded so you are never guessing.

Is this temperature converter free?

Yes. It runs in your browser with no account and no usage limits, covering Celsius, Fahrenheit, Kelvin, Rankine and Réaumur. An embeddable version is available too, so weather, science and cooking sites can host it without sending readers off-site.

Sumber dan Rujukan

  1. BIPM SI Brochure (9th edition, §2.3.1) — defines the kelvin as the SI base unit for thermodynamic temperature, anchored via the fixed Boltzmann constant k = 1.380649 × 10⁻²³ J/K exact
  2. 13th CGPM (1967) Resolution 4 — fixed 0 °C = 273.15 K exact and formally dropped the degree symbol from the kelvin ("100 K", not "100 °K")
  3. BIPM — 2019 revision of the SI (in force 20 May 2019): anchored the kelvin to the fixed Boltzmann constant k = 1.380649 × 10⁻²³ J/K exact, replacing the triple-point-of-water definition
  4. ISO 80000-5:2019 — Quantities and units, Part 5: Thermodynamics (codifies the kelvin, Celsius, Fahrenheit, Rankine and Réaumur unit definitions and conversion conventions)
  5. NIST Guide to the SI, Appendix B — Conversion factors (kelvin/Celsius/Fahrenheit/Rankine conversion equations and engineering-default rounding conventions)
  6. Wikipedia — Kelvin (SI base unit; 2019 SI redefinition via Boltzmann constant; absolute zero at 0 K; written without degree symbol per 13th CGPM 1967)
  7. Wikipedia — Celsius (1742 Anders Celsius; modern definition 0 °C = 273.15 K exact via 13th CGPM 1967; standard temperature scale outside the United States and a few US-affiliated territories)
  8. Wikipedia — Fahrenheit (1724 Daniel Gabriel Fahrenheit; legal anchors 32 °F = 0 °C, 212 °F = 100 °C; slope 5/9 K per degree; everyday scale in the United States)
  9. Wikipedia — Rankine scale (1859 William John Macquorn Rankine; absolute scale with Fahrenheit degree size; 0 °R = 0 K, 491.67 °R = 273.15 K; used in US heat-transfer textbooks and legacy industrial pyrometry)
  10. Wikipedia — Réaumur scale (1731 René Antoine Ferchault de Réaumur; 0 °Ré = 0 °C, 80 °Ré = 100 °C exact; dominant in 18th-19th C continental Europe — cited in Tolstoy's War and Peace and period French/German cookbooks)

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