To convert Celsius to Fahrenheit, multiply by 9/5 (1.8) and add 32: °F = °C × 1.8 + 32. So 20 °C is 20 × 1.8 + 32 = 68 °F. To go the other way, subtract 32 and divide by 1.8: °C = (°F − 32) ÷ 1.8. That’s the form given in NIST Special Publication 811, the US reference for unit conversions.
Why does the Celsius to Fahrenheit formula work? #
The two scales disagree on both the size of a degree and where zero sits. Two fixed points show the relationship. At standard atmospheric pressure:
| Celsius | Fahrenheit | |
|---|---|---|
| Water freezes | 0 °C | 32 °F |
| Water boils | 100 °C | 212 °F |
| Span | 100 degrees | 180 degrees |
The same physical span is 100 Celsius degrees and 180 Fahrenheit degrees, so one Celsius degree is 180/100 = 1.8 Fahrenheit degrees. That’s the multiplier. Fahrenheit’s freezing point sits at 32 instead of 0, so you add 32 after scaling. Going back, you undo the steps in reverse order: take off the 32 first, then divide.
Worked examples #
A 25 °C day. 25 × 1.8 = 45, plus 32 = 77 °F.
A European recipe says 180 °C. 180 × 1.8 = 324, plus 32 = 356 °F. American recipes round this to 350 °F.
−10 °C in winter. −10 × 1.8 = −18, plus 32 = 14 °F.
An American recipe says 350 °F. 350 − 32 = 318, divided by 1.8 = 176.7 °C. European recipes round this to 175 or 180 °C.
Is there a mental shortcut for Celsius to Fahrenheit? #
The popular one is double it and add 30. It’s close for mild weather and badly wrong at the extremes:
| °C | Exact °F | “Double + 30” | Error |
|---|---|---|---|
| −20 | −4 | −10 | 6 °F low |
| 0 | 32 | 30 | 2 °F low |
| 10 | 50 | 50 | exact |
| 20 | 68 | 70 | 2 °F high |
| 30 | 86 | 90 | 4 °F high |
| 40 | 104 | 110 | 6 °F high |
| 100 | 212 | 230 | 18 °F high |
| 180 | 356 | 390 | 34 °F high |
Fine for deciding whether you need a jacket. Useless for an oven.
A shortcut that’s exact takes one more step: double it, subtract 10% of the result, add 32. Doubling and taking off a tenth is the same as multiplying by 1.8. For 30 °C: double to 60, subtract 6 to get 54, add 32 for 86 °F. Exactly right, and still easy in your head.
For Fahrenheit to Celsius, the rough version is subtract 30 and halve. 80 °F becomes 50 ÷ 2 = 25 °C (the exact answer is 26.7 °C). It drifts the same way the forward shortcut does, so don’t use it above body temperature.
Celsius to Fahrenheit chart #
| °C | °F | °C | °F | |
|---|---|---|---|---|
| −40 | −40 | 20 | 68 | |
| −30 | −22 | 22 | 71.6 | |
| −20 | −4 | 25 | 77 | |
| −10 | 14 | 30 | 86 | |
| −5 | 23 | 35 | 95 | |
| 0 | 32 | 37 | 98.6 | |
| 5 | 41 | 40 | 104 | |
| 10 | 50 | 50 | 122 | |
| 15 | 59 | 100 | 212 |
37 °C, the traditional figure for normal body temperature, is exactly 98.6 °F.
Fahrenheit to Celsius chart for everyday temperatures #
| °F | °C |
|---|---|
| 0 | −17.8 |
| 20 | −6.7 |
| 32 | 0 |
| 40 | 4.4 |
| 50 | 10 |
| 60 | 15.6 |
| 68 | 20 |
| 72 | 22.2 |
| 80 | 26.7 |
| 90 | 32.2 |
| 100 | 37.8 |
Oven temperature conversion chart #
Recipes round oven temperatures to the nearest convenient number, and ovens aren’t that precise anyway. The exact values are in the middle column.
| °F (US recipe) | Exact °C | Usual °C on a recipe |
|---|---|---|
| 250 | 121.1 | 120 |
| 275 | 135 | 140 |
| 300 | 148.9 | 150 |
| 325 | 162.8 | 160 or 170 |
| 350 | 176.7 | 175 or 180 |
| 375 | 190.6 | 190 |
| 400 | 204.4 | 200 |
| 425 | 218.3 | 220 |
| 450 | 232.2 | 230 |
| 500 | 260 | 260 |
European recipes often give a second, lower temperature for fan (convection) ovens. Use the one that matches your oven rather than converting the other and adjusting it yourself.
Why is a temperature change different from a temperature? #
This catches a lot of people. The +32 only applies to a temperature reading, not to a difference between two readings. If the forecast says it’ll be 5 °C warmer tomorrow, that’s 5 × 1.8 = 9 °F warmer, not 41 °F. A thermostat setting nudged up by 2 °C is 3.6 °F. For changes, multiply or divide by 1.8 and skip the 32.
Where do −40 and Kelvin fit in? #
At −40, the two scales meet: −40 °C is exactly −40 °F. It’s the only temperature where that happens, and a handy check that you’ve applied the formula the right way round.
Kelvin is the SI unit of temperature. It uses Celsius-sized degrees but starts at absolute zero, so K = °C + 273.15. Water freezes at 273.15 K and boils at 373.15 K. Kelvin doesn’t use a degree sign. Absolute zero, 0 K, is −273.15 °C or −459.67 °F.
Rankine is the Fahrenheit equivalent of Kelvin, still used in some American engineering work: °R = °F + 459.67.
We explain how kelvin fits with the other SI base units in how the metric system works, and why the US still reads Fahrenheit in why the US uses the imperial system.
Converting temperatures on your phone #
Convert Units Calculator converts between Celsius, Fahrenheit and Kelvin with the real formulas rather than a single multiplier, which is why its answers come out right for the offset scales. Type 350 with °F selected and it shows 176.67 °C, with kelvin worked out underneath (449.82 K). Version 1.0.5 adds Rankine. It works offline, so it’s handy abroad when a weather app shows only the local scale.
For other units side by side, the metric to imperial conversion chart collects the common ones on one page.
Frequently asked questions #
What is 37 °C in Fahrenheit? #
37 °C is 98.6 °F. Multiply 37 by 1.8 to get 66.6, then add 32.
What is 180 °C in Fahrenheit? #
180 °C is 356 °F. American recipes treat it as 350 °F, the closest standard oven setting.
At what temperature are Celsius and Fahrenheit the same? #
At −40. Set °F equal to °C in the formula and solve: C = 1.8C + 32 gives −0.8C = 32, so C = −40.
What is 0 °F in Celsius? #
0 °F is −17.8 °C. Subtract 32 to get −32, then divide by 1.8.
Is it 9/5 or 5/9? #
Both, depending on direction. Celsius to Fahrenheit multiplies by 9/5 (1.8) and then adds 32. Fahrenheit to Celsius subtracts 32 first and then multiplies by 5/9 (divides by 1.8).