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Formula
°F = °C × 9/5 + 32
- °C
- the temperature in degrees Celsius
- 9/5
- 1.8, because a Celsius degree is 1.8 times as large as a Fahrenheit degree
- 32
- the offset, because water freezes at 0 °C but 32 °F
How to convert Celsius to Fahrenheit
The Celsius to Fahrenheit formula has two parts: a scale and a shift.
- Scale by 9/5 (1.8). A Celsius degree is bigger: water’s freezing-to-boiling range is 100 °C but 180 °F, and 180 ÷ 100 = 1.8.
- Shift by 32. The scales don’t start at the same place. Water freezes at 0 °C but 32 °F, so add 32 after scaling.
Worked through for a 26 °C beach day: 26 × 1.8 = 46.8, then 46.8 + 32 = 78.8 °F. The converter above shows these same two lines for whatever you type, so you can follow or copy the working.
Using this °C to °F converter
Type the Celsius reading, including a minus sign for frost, and the Fahrenheit answer appears at once with both steps of the working. Below it you’ll find the double-plus-30 estimate and how many degrees it misses by, which is a quick way to train your mental math. The dropdowns also let you start from Fahrenheit or convert to kelvin.
The “double it and add 30” shortcut
For a quick estimate, double the Celsius number and add 30. It works because doubling is close to × 1.8 and 30 is close to 32. The two errors cancel exactly at 10 °C, so the shortcut is spot-on for a cool spring morning and drifts the further you go from it:
| Celsius | Exact Fahrenheit | Double + 30 | Off by |
|---|---|---|---|
| −20 °C | −4 °F | −10 °F | 6 °F low |
| 0 °C | 32 °F | 30 °F | 2 °F low |
| 10 °C | 50 °F | 50 °F | exact |
| 20 °C | 68 °F | 70 °F | 2 °F high |
| 30 °C | 86 °F | 90 °F | 4 °F high |
| 40 °C | 104 °F | 110 °F | 6 °F high |
| 100 °C | 212 °F | 230 °F | 18 °F high |
For weather it’s close enough to decide on a jacket. For cooking or medicine, use the exact figure, which the converter gives alongside the estimate.
Celsius to Fahrenheit chart
Exact values calculated with the converter, from deep winter cold to boiling water.
| °C | °F | °C | °F | |
|---|---|---|---|---|
| −40 | −40 | 25 | 77 | |
| −30 | −22 | 35 | 95 | |
| −18 | −0.4 | 45 | 113 | |
| −10 | 14 | 50 | 122 | |
| −5 | 23 | 60 | 140 | |
| 0 | 32 | 70 | 158 | |
| 5 | 41 | 80 | 176 | |
| 15 | 59 | 90 | 194 |
−40 is the one point where both scales read the same number.
Oven temperatures: Celsius to Fahrenheit
European and Australian recipes give oven settings in Celsius, and many ovens outside the US have fan (convection) settings about 20 °C lower than conventional ones. US ovens are marked in 25 °F steps, so round to the nearest setting.
| Recipe says | Exact °F | Set a US oven to | Typical use |
|---|---|---|---|
| 140 °C | 284 °F | 275–285 °F | Slow roasting, meringues |
| 160 °C | 320 °F | 325 °F | Rich fruit cakes |
| 170 °C | 338 °F | 325–350 °F | Brownies, sponge cakes |
| 180 °C | 356 °F | 350 °F | Most cakes and cookies |
| 190 °C | 374 °F | 375 °F | Muffins, casseroles |
| 200 °C | 392 °F | 400 °F | Roast vegetables |
| 220 °C | 428 °F | 425 °F | Bread, roast potatoes |
| 230 °C | 446 °F | 450 °F | Pizza, crisping skin |
For food safety, the USDA lists safe internal temperatures in Fahrenheit: 165 °F (73.9 °C) for poultry and 160 °F (71.1 °C) for ground meat. When roasting a bird, the turkey cooking time calculator estimates how long it will take to get there.
Body temperature in Celsius and Fahrenheit
Thermometers sold outside the US read Celsius. These conversions are exact; what counts as normal depends on the person and the measuring site.
| °C | °F |
|---|---|
| 36 °C | 96.8 °F |
| 36.5 °C | 97.7 °F |
| 37 °C | 98.6 °F |
| 37.5 °C | 99.5 °F |
| 38 °C | 100.4 °F |
| 39 °C | 102.2 °F |
| 40 °C | 104 °F |
CDC guidance treats a measured temperature of 38 °C (100.4 °F) or above as a fever. For a high or persistent fever, or any fever in a young baby, call a doctor rather than relying on a chart.
Weather in Celsius: what to wear
- Below 0 °C (32 °F): freezing; ice on roads.
- 0–10 °C (32–50 °F): coat weather.
- 10–20 °C (50–68 °F): light jacket or sweater.
- 20–25 °C (68–77 °F): comfortable; T-shirt weather.
- Above 30 °C (86 °F): hot; stay hydrated.
Common mistakes
- Adding 32 first. (°C + 32) × 1.8 is wrong; scale first, then add 32.
- Using 9/5 for Fahrenheit to Celsius. Going back, subtract 32 and multiply by 5/9.
- Converting a change with the full formula. A rise of 5 °C is a rise of 9 °F, not 41 °F. Differences use × 1.8 only.
Worked examples
Comfortable room temperature
A thermostat set to 22 °C, in degrees Fahrenheit.
Inputs: Value = 22; From = Celsius (°C); To = Fahrenheit (°F)
°F = °C × 9/5 + 32 22 × 9/5 + 32 = 39.6 + 32 = 71.6 °F
Answer: 22 °C = 71.6 °F
A fever reading
A thermometer shows 38.5 °C. What is that in Fahrenheit?
Inputs: Value = 38.5; From = Celsius (°C); To = Fahrenheit (°F)
°F = °C × 9/5 + 32 38.5 × 9/5 + 32 = 69.3 + 32 = 101.3 °F
Answer: 38.5 °C = 101.3 °F
Below freezing
A winter forecast of −12 °C, where the "double and add 30" shortcut is furthest off.
Inputs: Value = -12; From = Celsius (°C); To = Fahrenheit (°F)
°F = °C × 9/5 + 32 (−12) × 9/5 + 32 = −21.6 + 32 = 10.4 °F
Answer: −12 °C = 10.4 °F
Absolute zero (edge case)
The coldest temperature possible; anything lower is rejected.
Inputs: Value = -273.15; From = Celsius (°C); To = Fahrenheit (°F)
°F = °C × 9/5 + 32 (−273.15) × 9/5 + 32 = −491.67 + 32 = −459.67 °F
Answer: −273.15 °C = −459.67 °F
Assumptions and limitations
- Uses the exact relationship °F = °C × 9/5 + 32. The answer is shown to up to 6 decimal places.
- The "double it and add 30" estimate is exact only at 10 °C (50 °F). It drifts by 1 °F for every 5 °C away from 10 °C, so the converter shows how far off it is.
- You can also convert from Fahrenheit or kelvin, or to kelvin. Temperatures below absolute zero (−273.15 °C) are rejected.
- Body-temperature figures are for unit conversion only, not medical advice. Contact a health professional about a fever, especially in infants.
Frequently asked questions
What is the formula for Celsius to Fahrenheit?
°F = °C × 9/5 + 32. Multiply by 9, divide by 5 (or multiply by 1.8), then add 32. For 15 °C, 15 × 1.8 = 27 and 27 + 32 = 59 °F.
What is the easiest way to convert Celsius to Fahrenheit in your head?
Double the Celsius number and add 30. 18 °C becomes 36 + 30 = 66 °F (exact 64.4 °F). It is close for weather temperatures but too high for hot ovens.
What is 180 °C in Fahrenheit?
356 °F. UK and European recipes that say 180 °C are usually followed at 350 °F in the US, since ovens are set in 25 °F steps.
What is normal body temperature in Fahrenheit?
The traditional figure is 37 °C, or 98.6 °F, though normal varies by person, time of day and where it is measured. CDC guidance treats 38 °C (100.4 °F) or higher as a fever.
Is 30 degrees Celsius hot?
Yes. 30 °C is 86 °F, a hot summer day. 20 °C (68 °F) is mild, and 10 °C (50 °F) calls for a jacket.
How do you convert Fahrenheit back to Celsius?
Subtract 32, then multiply by 5/9. 77 °F − 32 = 45, and 45 × 5/9 = 25 °C. Swap the units in the converter, or use the [temperature converter](/temperature-converter/) for kelvin as well.
Sources
- SI Units – Temperature — National Institute of Standards and Technology (NIST). Checked October 12, 2026.
- Definitions of Signs, Symptoms, and Conditions of Ill Travelers — Centers for Disease Control and Prevention (CDC). Checked October 12, 2026.
- Safe Minimum Internal Temperature Chart — USDA Food Safety and Inspection Service. Checked October 12, 2026.