Convert Fahrenheit to Celsius
Translate Fahrenheit temperatures into Celsius for metric weather, international recipes and converting US thermostat settings to °C.
1 °F = -17.2222 °C
To convert Fahrenheit to Celsius, subtract 32 and multiply by 5/9: °C = (°F − 32) ÷ 1.8. So 70 °F = 21.1 °C and 98.6 °F = 37 °C. The subtraction must come first — reversing the order of operations is the single most common mistake in this conversion and produces answers that are wildly wrong. Dividing by two after subtracting 30 is a workable estimate in weather ranges: 80 °F gives 25 against the true 26.7. The reference points most people need are 32 °F freezing, 68 °F room temperature, 98.6 °F body temperature and 212 °F boiling. Two cautions. A fever threshold of 100.4 °F is exactly 38 °C, and rounding it to 38.5 changes clinical meaning. And a temperature difference converts differently from a temperature: a rise of 18 °F is a rise of 10 °C, with no offset applied.
Quick reference: fahrenheit to celsius
| Fahrenheit | Celsius |
|---|---|
| -40 | −40 °C (scales meet) |
| 0 | −17.8 °C |
| 32 | 0 °C (freezing) |
| 50 | 10 °C |
| 68 | 20 °C (room temp) |
| 98.6 | 37 °C (body temp) |
| 100.4 | 38 °C (fever) |
| 212 | 100 °C (water boils) |
| 350 | 176.7 °C (oven) |
How do you convert fahrenheit to celsius?
Formula: °C = (°F − 32) × 5/9 • A 70 °F thermostat setting → (70 − 32) ÷ 1.8 = 21.1 °C. • A 98.6 °F body temperature → (98.6 − 32) ÷ 1.8 = 37 °C exactly. • A 350 °F oven → (350 − 32) ÷ 1.8 = 176.7 °C, which European recipes round to 180 °C. • A 100 °F hot day → (100 − 32) ÷ 1.8 = 37.8 °C.
When and why people use fahrenheit to celsius
Reading US sources is the main reason. American weather reports, thermostat settings, recipes, appliance manuals and industrial specifications all use Fahrenheit, and anyone outside that system needs the conversion to interpret them. The mental anchors worth memorising are 32 °F = 0 °C, 50 °F = 10 °C, 68 °F = 20 °C and 86 °F = 30 °C — four points that let you estimate anything in between. Cooking again produces the most frequent practical use, in reverse: US recipes specify 350 °F, 375 °F and 400 °F, which convert to 177 °C, 191 °C and 204 °C and are normally rounded to 180 °C, 190 °C and 200 °C respectively. Health is the third. A US thermometer reading of 100.4 °F is the standard fever threshold and converts to exactly 38 °C, which is why that oddly specific decimal appears in guidance written for both systems.
Common mistakes to watch for when converting fahrenheit to celsius
Order of operations is the dominant error: dividing by 1.8 before subtracting 32 gives a completely wrong figure. For 100 °F the correct answer is 37.8 °C, but subtracting after dividing produces 23.6 °C. A second issue is applying the full formula to a temperature difference — a 10 °F change is a 5.6 °C change, calculated with the 1.8 divisor alone and no offset. Third, US recipes and European ovens rarely line up on round numbers, so converted oven temperatures almost always need rounding to the nearest available setting; going up rather than down is usually safer for baking. Finally, some US industrial specifications quote Rankine rather than Fahrenheit for absolute temperatures, which is a different scale again with its zero at absolute zero.
How to estimate fahrenheit to celsius in your head
Subtract 30 and then halve. For 70 °F: 70 − 30 = 40, halved is 20 °C against a true 21.1. The method is quick and runs about a degree low in the middle of the everyday range. For a closer figure, subtract 32 and then take half plus a further tenth of that half. For 70 °F: 70 − 32 = 38, half is 19, a tenth of 19 is 1.9, giving 20.9 °C against a true 21.1. Anchors: 32 °F = 0 °C, 50 °F = 10 °C, 68 °F = 20 °C, 86 °F = 30 °C, 104 °F = 40 °C. Each 18 °F step is a 10 °C step, which is the cleanest way to interpolate. For oven temperatures the estimate is fine because ovens are imprecise anyway; for anything medical use the exact formula.
Fahrenheit to Celsius FAQ
What is the formula?
- °C = (°F − 32) × 5/9. Subtract 32 first, then divide by 1.8.
What is 70 °F in Celsius?
- 21.1 °C — a comfortable indoor temperature.
Why does order of operations matter?
- Dividing before subtracting gives a wrong answer. For 100 °F the correct result is 37.8 °C; doing it backwards yields 23.6 °C.
How do I convert a difference in Fahrenheit?
- Divide by 1.8 and skip the offset. A 10 °F change equals a 5.6 °C change.
What is 350 °F in Celsius?
- 176.7 °C, which recipes normally round up to 180 °C.
What is normal body temperature?
- 98.6 °F, which is exactly 37 °C.
What is Rankine?
- An absolute scale using Fahrenheit-sized degrees with zero at absolute zero. It appears in some US engineering work and is not the same as Fahrenheit.
Why does the US still use Fahrenheit?
- Historical inertia rather than any technical merit. The scale was already embedded in weather reporting, appliances and building codes before metrication efforts began, and no mandatory switch was ever completed.
What Fahrenheit range is comfortable indoors?
- Roughly 68 to 72 °F, which is 20 to 22 °C. Below 64 °F (18 °C) most people find a room cool, and above 78 °F (26 °C) uncomfortably warm.
Does the tool upload my values?
- No. Everything is calculated locally in the page.
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Sources: NIST Special Publication 811; BIPM SI brochure; CDC guidance defining fever as 100.4 °F (38.0 °C).