Convert Fahrenheit to Celsius
Convert Fahrenheit to Celsius instantly. Formula, worked examples and a full reference table from -40° upward.
Last updated
Converting Fahrenheit to Celsius is not a simple multiplication, because the two scales have different zero points as well as different degree sizes. The conversion needs both a scaling step and an offset.
Enter any temperature above and the result updates as you type. The formula and a reference table covering everyday temperatures follow below.
Temperature is the one category where conversion is not multiplication. The scales have different zero points as well as different degree sizes, so every conversion needs an offset too, and no single "factor" exists to quote. It is also the conversion people most often need at speed — a weather forecast, an oven setting, a fever reading — which is why the approximations are worth knowing: doubling Celsius and adding 30 gets you within a couple of degrees of Fahrenheit across everyday temperatures.
Fahrenheit to Celsius formula
To go the other way, use °F = (°C × 9/5) + 32.
About these units
Fahrenheit puts water's freezing and boiling points at 32 and 212, giving 180 degrees between them. A Fahrenheit degree is therefore smaller than a Celsius one.
The Celsius scale sets zero at the freezing point of water and 100 at its boiling point, both at standard atmospheric pressure.
Sources
- NIST Special Publication 811, Guide for the Use of the International System of Units (SI), 2008 edition — conversion factors for units outside the SI.
- Preston-Thomas, "The International Temperature Scale of 1990 (ITS-90)", Metrologia 27(1), 1990.
- Bureau International des Poids et Mesures, The International System of Units (SI), 9th edition, 2019.
Fahrenheit to Celsius conversion table
| Fahrenheit | Celsius |
|---|---|
| -40 °F | -40 °C |
| -20 °F | -28.8889 °C |
| -10 °F | -23.3333 °C |
| 0 °F | -17.7778 °C |
| 10 °F | -12.2222 °C |
| 20 °F | -6.6667 °C |
| 25 °F | -3.8889 °C |
| 30 °F | -1.1111 °C |
| 37 °F | 2.7778 °C |
| 40 °F | 4.4444 °C |
| 50 °F | 10 °C |
| 100 °F | 37.7778 °C |
Frequently asked questions
How many celsiuses are in a fahrenheit? +
Temperature scales cannot be compared this way, because they do not share a zero point. Use the formula °C = (°F − 32) × 5/9 instead.
What is 25 °F in °C? +
25 °F equals -3.8889 °C. Apply the formula °C = (°F − 32) × 5/9.
How do I convert celsius back to fahrenheit? +
Use °F = (°C × 9/5) + 32. The converter above handles both directions, or see our dedicated Celsius to Fahrenheit page.
How accurate is this fahrenheit to celsius conversion? +
The scale definitions are exact — the relationships between Celsius, Fahrenheit and Kelvin are fixed by definition rather than measured — and the calculation carries full double precision. Only the displayed result is rounded, so what you read is a rounded view of an exact conversion rather than a conversion performed on rounded numbers.
Is there a quick way to estimate °F to °C in my head? +
Subtract 30 and halve it. The result is a degree or two low across the everyday range, and the error grows only at extremes well outside normal weather.