Fahrenheit to Celsius Formula

The inverse of °F = (°C × 9/5) + 32 is °C = (°F − 32) × 5/9.

Why subtract 32 first?

32°F is the ice point. Subtracting 32 measures how far you are from that point in Fahrenheit degrees. Then 5/9 compresses those degrees onto the Celsius scale (100 Celsius degrees span the same interval as 180 Fahrenheit degrees).

If you multiply the raw Fahrenheit reading by 5/9, the offset is still inside the number and the result is wrong.

Steps

1. Subtract 32 from the Fahrenheit reading.
2. Multiply by 5/9.
3. The result is Celsius.

Three numerical examples

• 32°F: (32 − 32) × 5/9 = 0°C
• 77°F: (77 − 32) × 5/9 = 45 × 5/9 = 25°C
• 212°F: (212 − 32) × 5/9 = 100°C

A mental shortcut — subtract 30 and divide by 2 — is only a rough indoor estimate (72°F ≈ 21°C vs actual 22.2°C).

Common mistakes

• Multiplying by 5/9 before subtracting 32.
• Treating 98.6°F as 37°C rounded incorrectly to 99 or 100.
• Using this formula on a temperature difference. For ΔT, skip the −32 and use 5/9 only.

Try the numbers

Fahrenheit to Celsius converter · Temperature Converter · reverse explainer: Celsius to Fahrenheit Formula