Celsius to Fahrenheit: The Formula

The formula

The conversion has two steps: scale, then shift. Multiply the Celsius value by 9/5 (that is 1.8) because a Fahrenheit degree is smaller — there are 180 of them between freezing and boiling versus 100 Celsius degrees. Then add 32, because Fahrenheit puts freezing at 32 rather than 0. So 20 °C becomes 20 × 1.8 + 32 = 68 °F, and body temperature 37 °C becomes 98.6 °F.

Going the other way

To convert Fahrenheit back to Celsius, reverse the two steps in reverse order: first subtract 32 to undo the shift, then multiply by 5/9 to undo the scale. So 68 °F is (68 − 32) × 5/9 = 36 × 0.556 = 20 °C. The order matters — subtract before you multiply. Getting comfortable with both directions means you can move between a US weather app and a European one without a second thought.

The quick mental shortcut

When you just want a feel for the number, double the Celsius and add 30. For 20 °C that gives 70 — close to the true 68. For 25 °C you get 80, near the exact 77. The shortcut works because doubling stands in for the ×1.8 and 30 approximates the +32; it drifts a few degrees at the extremes but is spot-on enough for weather. For anything precise — cooking, medicine, science — use the full 9/5 + 32.

Reference points worth knowing

A few fixed points make the scales instantly readable. Water freezes at 0 °C / 32 °F and boils at 100 °C / 212 °F. Normal body temperature is 37 °C / 98.6 °F. A warm room sits near 21 °C / 70 °F. And there is one neat curiosity: at −40°, the two scales meet — −40 °C is exactly −40 °F. Anchor a handful of these and most everyday temperatures fall into place without any arithmetic at all.

Frequently asked questions

What is 20°C in Fahrenheit?

68°F, from 20 × 9/5 + 32.

What's the easy way to convert Celsius to Fahrenheit?

Double the Celsius and add 30 for a rough answer; use ×9/5 + 32 for the exact one.

At what temperature are Celsius and Fahrenheit equal?

At −40°, both scales read the same.