Fahrenheit to Celsius Converter (°F, °C, K)

To convert Fahrenheit to Celsius, subtract 32 and divide by 1.8: °C = (°F − 32) ÷ 1.8. For 72 °F, (72 − 32) ÷ 1.8 = 40 ÷ 1.8 ≈ 22.22 °C. To go back, multiply by 1.8 and add 32, so 25 °C × 1.8 + 32 = 77 °F. For kelvins, add 273.15 to the Celsius value: 22.22 °C ≈ 295.37 K.

How to use the temperature converter

1. Type a temperature. Negative numbers and decimals are fine.
2. Choose the unit you have under From (°F, °C, K or °R) and the unit you want under To. The ⇄ button swaps them.
3. Read the answer, all four scales, the formula with your numbers, the quick mental estimate with its error, and where the reading sits on a thermometer.
4. Use the Change tab for a rise or drop (such as “18 °F warmer”), and the Chart tab to print a conversion table for any range and step.

Fahrenheit to Celsius formula

The exact formula, as published by NIST, is:

°C = (°F − 32) ÷ 1.8

Two things happen in it. Subtracting 32 lines up the zero points, because water freezes at 32 °F but at 0 °C. Dividing by 1.8 changes the size of the degrees: one Celsius degree is as big as 1.8 Fahrenheit degrees, so the same temperature needs fewer of them. You may also see the formula written as (°F − 32) × 5/9. That is the same thing, because 1 ÷ 1.8 = 5/9.

The order matters. Subtract 32 first, then divide. Dividing first gives a wrong answer for every temperature.

Celsius to Fahrenheit formula

Undo the steps in reverse order: multiply by 1.8, then add 32.

°F = °C × 1.8 + 32

For 37 °C: 37 × 1.8 = 66.6, and 66.6 + 32 = 98.6 °F.

Kelvin and Rankine

Kelvin is the SI unit of temperature. Its zero is absolute zero, the coldest possible temperature, so kelvins are never negative. A kelvin is the same size as a Celsius degree, and 0 °C is exactly 273.15 K. Rankine is the absolute scale with Fahrenheit-sized degrees: 0 °R is absolute zero and 1 °R is the same size as 1 °F.

Absolute zero is 0 K = −273.15 °C = −459.67 °F = 0 °R. The converter flags any input below it.

Worked examples

Example 1: an oven at 350 °F

(350 − 32) ÷ 1.8 = 318 ÷ 1.8 = 176.67 °C. Recipes and oven dials round this to 180 °C, which is close enough for baking.

Example 2: a 25 °C day in Fahrenheit

25 × 1.8 = 45, then 45 + 32 = 77 °F.

Example 3: 300 K in Celsius and Fahrenheit

300 − 273.15 = 26.85 °C. Then 26.85 × 1.8 + 32 = 48.33 + 32 = 80.33 °F.

Quick mental math: double and add 30

For a fast Celsius to Fahrenheit estimate, double the Celsius number and add 30. To go from Fahrenheit to Celsius, subtract 30 and halve. The shortcut uses 2 instead of 1.8 and 30 instead of 32, so it is exact only at 10 °C (50 °F) and drifts by 1 °F for every 5 °C away from that point. The converter shows the estimate next to the exact answer so you can see the error.

The trick works well for weather. For ovens and anything scientific, use the exact formula.

Converting a temperature change

A change is not converted like a reading. If the forecast says it will be 18 °F warmer, the rise in Celsius is 18 ÷ 1.8 = 10 °C. There is no 32 in it, because the 32 cancels out when you subtract one reading from another: 50 °F to 68 °F is 10 °C to 20 °C, a rise of 10 °C. NIST notes that an interval of one Celsius degree corresponds to 1.8 Fahrenheit degrees, and that a change of 1 °C equals a change of 1 K.

Common reference temperatures

The boiling point drops as you go higher because air pressure falls. Body temperature varies from person to person and through the day; the figure above is NIST’s rounded touchstone value, not medical guidance.

Oven temperature conversion with gas marks

Oven settings are rounded, not exact conversions. The first four columns are from the Which? oven temperature table; the last column is the exact conversion of the Fahrenheit setting. Fan (convection) ovens are usually set lower than conventional ones.

Safe cooking temperatures in °F and °C

The USDA Food Safety and Inspection Service gives these safe minimum internal temperatures, measured with a food thermometer. The Celsius values are exact conversions.

Common mistakes

• Dividing before subtracting. 72 ÷ 1.8 − 32 = 8 is wrong; (72 − 32) ÷ 1.8 = 22.22 is right.
• Using 32 on a temperature change. A 10 °C rise is an 18 °F rise, not 50 °F.
• Writing “degrees kelvin”. The unit is simply kelvin (K), with no degree sign.
• Treating oven conversions as exact. 180 °C is the standard setting for 350 °F, but the exact value is 176.67 °C.

Sources

All sources checked November 2026.

• NIST: SI Units – Temperature (kelvin definition, Celsius relation, exact conversions, touchstone temperatures)
• NIST Special Publication 811, Appendix B.9: conversion factors for temperature (Fahrenheit, Rankine, kelvin)
• USGS Yellowstone Volcano Observatory: How hot are Yellowstone’s boiling waters? (boiling point at sea level and at elevation)
• USDA Food Safety and Inspection Service: Safe Minimum Internal Temperature Chart
• Which?: Oven temperature conversion table (gas mark, °F, °C and fan)

Temperature Conversion practice quiz: 10 questions

Test yourself with 10 multiple-choice questions. Choose an answer and press Submit to see if you are right and why. Your score appears at the end.

Frequently asked questions

Is there an easy way to convert Fahrenheit to Celsius in your head?

Subtract 30 and halve. For 80 °F that gives 25 °C, while the exact answer is 26.67 °C. The estimate is closest near 50 °F and gets worse for very hot or very cold readings.

At what temperature are Fahrenheit and Celsius the same?

At −40. Setting °F = °C in °F = °C × 1.8 + 32 gives −0.8 × °C = 32, so °C = −40, and −40 °C = −40 °F.

What is 350 °F in Celsius?

Exactly 176.67 °C. Oven tables round it to 180 °C (about 160 °C in a fan oven), which is gas mark 4.

Why is 0 °C equal to 273.15 K and not 273 K?

The kelvin is defined through the Boltzmann constant, and the Celsius scale is defined as kelvins minus exactly 273.15. That offset puts 0 °C very close to the freezing point of water, while 0 K stays at absolute zero.

Is 98.6 °F the same as 37 °C?

Yes, 37 × 1.8 + 32 = 98.6 exactly. NIST lists body temperature as about 37 °C (99 °F) in its rounded table. Normal readings vary between people, so ask a health professional about a specific reading.

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