Temperature Converter
Convert instantly between Fahrenheit, Celsius, and Kelvin — enter a temperature in any scale and see the other two.
The conversion formulas
°C = (°F − 32) × 5/9
K = °C + 273.15
For a fast head-math conversion of Celsius to Fahrenheit, double it and add 30: 20°C ≈ 70°F (exact is 68°F). Good enough for checking the weather.
A recipe calls for 180°C: 180 × 9/5 + 32 = 324 + 32 = 356°F — most US recipes and dial ovens round this to the nearest common setting, 350°F.
Reference temperatures
| °C | °F | K | |
|---|---|---|---|
| Absolute zero | −273.15 | −459.67 | 0 |
| Water freezes | 0 | 32 | 273.15 |
| Room temperature | 21 | 70 | 294 |
| Body temperature | 37 | 98.6 | 310 |
| Water boils | 100 | 212 | 373.15 |
The two scales cross at −40° (−40°C = −40°F). Celsius and Kelvin share the same degree size — a change of 1°C equals a change of 1 K — while Fahrenheit degrees are smaller (1.8 per Celsius degree). Handy when following recipes, checking overseas weather, or reading science. For lengths and weights, see the length and weight converters.
Why three different scales exist
Fahrenheit was designed in the early 1700s around a brine mixture and human body temperature as reference points, which is why its numbers look arbitrary today. Celsius was defined later around water's freezing and boiling points at sea level, giving it the clean 0–100 range. Kelvin was built for science: it starts at absolute zero — the coldest temperature theoretically possible, where molecular motion stops — so it never needs negative numbers, which is why physics and chemistry formulas are almost always written in Kelvin.
Common temperature-conversion mistakes
- Using the "double and add 30" shortcut for precise or scientific work. It's accurate to within about 2°F in the everyday range (0-35°C) but drifts further outside that range — use the exact formula for cooking temps, medical readings, or anything precision-sensitive.
- Forgetting Fahrenheit and Celsius degrees are different sizes. A "10 degree" change means something different in each scale (10°C ≈ 18°F of change) — degree changes, unlike absolute temperatures, can't be converted with the +32 offset; only the 1.8 multiplier (or its inverse) applies.
- Mixing up Kelvin with Celsius when reading scientific data. A reported "300 K" is room temperature (about 27°C, 80°F), not 300°C — forgetting to subtract 273.15 when converting Kelvin back to Celsius is an easy and consequential mistake in lab or engineering contexts.
Frequently asked questions
How do I convert Celsius to Fahrenheit?
× 9/5 + 32. 20°C = 68°F.
Quick way to estimate C to F?
Double and add 30. 20°C ≈ 70°F.
What is Kelvin?
A scale starting at absolute zero; K = °C + 273.15.
Why does science use Kelvin instead of Celsius?
Kelvin starts at absolute zero, the theoretical point where molecular motion stops, so it never requires negative numbers. This makes physics and chemistry formulas involving temperature simpler and more consistent than using Celsius or Fahrenheit.
How do I convert an oven temperature from Celsius to Fahrenheit?
× 9/5 + 32. 180°C = 356°F, usually rounded to the nearest setting, 350°F.
How do I convert a temperature difference, not an absolute temperature?
Multiply the Celsius difference by 1.8 — don't add 32, since that offset only applies to absolute readings. A 10°C rise is an 18°F rise.
Related calculators
Last reviewed: September 2026.