How to convert fahrenheit to celsius
Temperature is the one conversion family with an offset as well as a ratio: remove the 32-degree offset first so both scales align at freezing, then rescale by 5/9 for the different degree size. The anchors check out exactly — 32 °F is 0 °C, 212 °F is 100 °C, and −40 is the same on both scales.
Fahrenheit anchors water's freezing at 32 and boiling at 212, putting 180 degrees between them where Celsius puts 100 — hence the 5/9 ratio — and its zero sits 32 degrees lower, hence the subtraction that must happen first. The order is the whole skill of this conversion: strip the offset, then rescale. Every other temperature pair on this site is a single multiplication; this one and its sibling are the two-step exceptions, and they are exact.
The famous numbers are all in the table: 98.6 °F is 37 °C, normal body temperature; 32 °F is 0 °C, a frost; 212 °F is 100 °C, boiling. Everyday weather fills the middle — 68 °F is a mild 20 °C, 86 °F a hot 30 °C, 104 °F a fever and a heatwave at 40 °C. This page's default, 100 °F, is 37.777778 °C: a very hot day, and a good demonstration that not every conversion lands on a tidy number.
The common mistake is rescaling before subtracting: (100 × 5/9) − 32 gives 23.6 instead of 37.8, an error big enough to misread a fever chart or a recipe. The mental shortcut “subtract 30 and halve” (100 °F → about 35) is a jacket-decision estimate only, drifting several degrees where it matters. And remember body-temperature judgements: a reading of 100.4 °F is the standard fever threshold precisely because it is 38 °C — thresholds like that are why the exact formula, not the shortcut, belongs on medical and cooking numbers.
Worked example
100 degrees Fahrenheit is 37.777778 degrees Celsius: (100 − 32) × 5/9 = 37.777778 — hotter than body temperature, whether you meet it as weather or on a thermometer.
How to use this converter
- Enter your value in fahrenheit in the box above — the result updates as you type.
- Read the converted value in celsius in the headline panel.
- Check the factor, the formula and the inverse result (your answer converted back) in the stats if you need to show your working.
- Use the Fahrenheit to Celsius conversion table below for other common values without typing each one.