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The formula is F = (C x 9/5) + 32. So 20 C = 68 F. For quick mental math: double the Celsius, subtract 10%, and add 32. Or just remember these anchors: 0 C = 32 F, 20 C = 68 F, 37 C = 98.6 F, 100 C = 212 F.
Temperature conversion trips people up because it is not a simple multiplication like kg-to-lbs or km-to-miles. The formula involves both multiplication and addition, which makes mental math harder. This guide breaks it down with a chart, the formula explained step by step, a mental math shortcut that actually works, and a free converter for when you want exact numbers instantly.
Temperature reference from -40 C to 100 C, with everyday context for each range.
| Celsius | Fahrenheit | Context |
|---|---|---|
| -40 C | -40 F | Extreme arctic cold (same on both scales) |
| -30 C | -22 F | Dangerously cold, frostbite risk |
| -20 C | -4 F | Very cold winter day |
| -10 C | 14 F | Cold winter day |
| -5 C | 23 F | Cold, near freezing |
| 0 C | 32 F | Water freezes |
| 5 C | 41 F | Refrigerator temperature |
| 10 C | 50 F | Cool autumn day, light jacket |
| 15 C | 59 F | Mild, comfortable with a sweater |
| 20 C | 68 F | Room temperature — comfortable |
| 25 C | 77 F | Warm, pleasant day |
| 30 C | 86 F | Hot summer day |
| 35 C | 95 F | Very hot, heat advisory range |
| 37 C | 98.6 F | Normal body temperature |
| 38 C | 100.4 F | Fever threshold |
| 40 C | 104 F | High fever / extremely hot day |
| 45 C | 113 F | Extreme heat (Death Valley range) |
| 50 C | 122 F | Hot tub upper limit |
| 100 C | 212 F | Water boils |
These are the numbers worth memorizing. They cover almost every temperature conversation you will have.
| What | Celsius | Fahrenheit |
|---|---|---|
| Water freezes | 0 C | 32 F |
| Refrigerator | 3 to 5 C | 37 to 41 F |
| Cool day | 10 C | 50 F |
| Room temperature | 20 to 22 C | 68 to 72 F |
| Warm day | 25 C | 77 F |
| Hot day | 30 C | 86 F |
| Body temperature | 37 C | 98.6 F |
| Fever starts | 38 C | 100.4 F |
| High fever | 40 C | 104 F |
| Water boils | 100 C | 212 F |
| Oven: moderate | 180 C | 350 F |
| Oven: hot | 200 C | 400 F |
| Oven: very hot | 230 C | 450 F |
The Celsius-to-Fahrenheit formula is: F = (C x 9/5) + 32
Breaking it down:
Example: Convert 25 C to Fahrenheit.
To go the other direction (F to C): C = (F - 32) x 5/9
Example: Convert 72 F to Celsius.
The "double, subtract 10%, add 32" trick works surprisingly well for Celsius to Fahrenheit:
Example: Convert 30 C to Fahrenheit.
Exact answer: 86 F. The shortcut is dead-on.
Why does this work? Multiplying by 2 and subtracting 10% is the same as multiplying by 1.8, which is 9/5. The shortcut replaces the fraction with simple arithmetic.
For Fahrenheit to Celsius, reverse it: subtract 32, halve it, add about 10%. 98 F: 98 - 32 = 66, halved = 33, plus 10% (3.3) = 36.3 C. Exact: 36.7 C. Close enough for any conversation.
Daniel Fahrenheit created his scale in 1724, using the coldest temperature he could create in his lab (a salt-ice mixture) as 0 and human body temperature as roughly 96 (later corrected to 98.6). The scale is somewhat arbitrary.
Anders Celsius created his scale in 1742, anchoring it to water: 0 degrees where water freezes and 100 degrees where water boils. The metric logic (base-10 between two universal reference points) made it the standard for science and eventually most of the world.
The US inherited Fahrenheit from the British colonies and never switched. Almost every other country moved to Celsius during the metrication waves of the 19th and 20th centuries.
Oven temperatures are the most common practical conversion. Most recipes from the US use Fahrenheit, while recipes from Europe, Australia, and most other countries use Celsius.
When traveling between Fahrenheit and Celsius countries, these ranges help you read the forecast:
Understanding body temperature across scales matters for medical situations:
For completeness: Kelvin is the temperature scale used in science. It starts at absolute zero (the coldest possible temperature, where all molecular motion stops) and uses the same degree size as Celsius. To convert: K = C + 273.15. So 0 C = 273.15 K, and absolute zero is -273.15 C (-459.67 F). You will only encounter Kelvin in physics, chemistry, and astronomy.
Convert Celsius to Fahrenheit (or F to C) instantly — no formula memorization needed.
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