What this calculator does
Turn a Celsius temperature into Fahrenheit, or the other way around, in one step. Celsius is the metric scale, used in almost every weather forecast outside the United States. Fahrenheit is the everyday scale in the US and a few other places. It's on weather reports, thermostats, ovens and fever thermometers. Recipes, travel forecasts and appliance manuals often need changing from one to the other.
This one takes two moves, not one. The degrees are different sizes: one Celsius degree equals 1.8 Fahrenheit degrees. And the scales start in different places: 0 °C is 32 °F. The converter does both parts in the right order and shows each step. It also gives the quick "double it and add 30" guess, so you can see how close that gets. Below the result is a chart from −40 to 250 °C (or −40 to 500 °F), marked with everyday temperatures.
Where it's used
Why this math matters outside the classroom:
- Travel weather. A forecast of 25 °C abroad works out to 25 × 9 ÷ 5 + 32 = 77 °F.
- Baking. Bakers using a European recipe find 180 °C is 356 °F and usually set the oven to 350 °F.
- Freezing point. Students check the formula with water's freezing point, 0 °C, which gives 32 °F.
- Lab reports. A culture kept at 37 °C is described as 98.6 °F when the results are shared with readers used to Fahrenheit.
- Where scales meet. At −40 the two scales agree, since −40 × 9 ÷ 5 + 32 = −40.
Grade level and standards: Grades 6–7; Common Core State Standards for Mathematics 6.EE.A.2.c. © Copyright 2010. National Governors Association Center for Best Practices and Council of Chief State School Officers. All rights reserved.
How to use it
- Enter the temperature. Negative numbers and decimals are fine, down to absolute zero, the coldest anything can get.
- Choose Celsius to Fahrenheit or Fahrenheit to Celsius.
- Read the exact answer, follow the two steps, and compare it with the quick mental guess.
- Open the chart under the result for weather, fridge, body and oven temperatures.
What the inputs mean
- Temperature
- A thermometer reading in °C (for °C → °F) or °F (for °F → °C). Nothing can be colder than absolute zero (−273.15 °C or −459.67 °F), so readings below it aren't accepted.
- Direction
- Choose which scale you're starting from.
Formula and method
°F = °C × 9/5 + 32 = °C × 1.8 + 32 °C = (°F − 32) × 5/9 = (°F − 32) ÷ 1.8 quick estimate: °F ≈ °C × 2 + 30; °C ≈ (°F − 30) ÷ 2
In the formulas, °C is the Celsius temperature and °F is the Fahrenheit temperature. The ≈ sign means "about equal to".
Water freezes at 0 °C, which is 32 °F. It boils at 100 °C, which is 212 °F, at sea level. So 100 Celsius degrees cover the same gap as 180 Fahrenheit degrees. That makes each Celsius degree 180/100 = 9/5 = 1.8 Fahrenheit degrees.
Going from Celsius, multiply first, then add 32. Going from Fahrenheit, take away the 32 first, then multiply by 5/9. Doing these in the wrong order is the most common mistake.
Worked example
A forecast says 20 °C. What is that in Fahrenheit?
- Multiply by 9/5: 20 × 9/5 = 36.
- Add 32: 36 + 32 = 68.
- Quick check: double 20 is 40, plus 30 is 70, which is 2 °F high.
Result: 20 °C is exactly 68 °F, a mild room temperature. The mental shortcut gives 70 °F.
Understanding the result
Here's a handy mental shortcut: double the Celsius number and add 30. At 10 °C it's exact (50 °F). At 30 °C it gives 90, while the true answer is 86 °F. At −10 °C it gives 10, while the true answer is 14 °F.
The shortcut is off by 0.2 °F for every degree you move away from 10 °C. So it's fine for weather, but not for baking. To go the other way, from Fahrenheit, subtract 30 and then halve.
Some useful reference points: −40 °C = −40 °F, where the two scales meet. 0 °C = 32 °F. 20 °C = 68 °F. 37 °C = 98.6 °F, the textbook body temperature. 100 °C = 212 °F.
For ovens: 180 °C = 356 °F (usually set as 350 °F), 200 °C = 392 °F (400 °F) and 220 °C = 428 °F (425 °F).
A change in temperature works differently. A rise of 10 °C is a rise of 18 °F, using only the 9/5 part. Adding 32 is for readings, not for differences.
Assumptions and limitations
- The number you enter is a temperature reading, not a change in temperature.
- To convert a change in temperature, use only the 9/5 part, without adding or taking away 32.
- Oven dials go up in rounded steps, so round a converted oven temperature to the nearest setting.
Frequently asked questions
What is 350 °F in Celsius?
(350 − 32) × 5/9 = 176.67 °C. Celsius recipes usually round it to 180 °C. That's a gap of about 3 °C, and ovens don't hold an exact temperature anyway.
Is there a temperature that is the same in both scales?
Yes: −40. If you set C × 9/5 + 32 equal to C and solve, you get C = −40. So −40 °C and −40 °F are the same temperature.
Why is 98.6 °F given as normal body temperature?
It's 37 °C converted exactly. Real readings change through the day and depend on where you measure. So treat it as a reference point, not a cutoff.
What is 100 °F in Celsius?
(100 − 32) × 5/9 = 37.78 °C. Going the other way, 40 °C is 104 °F. So a day in the low 100s Fahrenheit is around 38 to 40 °C.
What oven temperature is 200 °C in Fahrenheit?
200 × 9/5 + 32 = 392 °F, which most recipes round to 400 °F. In the same way, 180 °C = 356 °F (set 350 °F) and 220 °C = 428 °F (set 425 °F). For a fan or convection oven, recipes often say to go about 20 °C (25 °F) lower. Follow the recipe or your oven's manual.
Why does 1.8 appear instead of 9/5?
They're the same number. 9 ÷ 5 = 1.8, and 5/9 is about 0.5556.
How this calculator is checked
Method: Scale definitions: °F = °C × 9/5 + 32 (exact). The calculation is covered by automated tests with known reference values and edge cases. Last updated 2026-10-18. Found a problem? Tell us.
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