40°C to Fahrenheit
40°C = 104°F — step-by-step calculation
40°C
=
104°F
F = C × 9/5 + 32
40 × 9/5 + 32
= 72 + 32
= 104°F
Conversion curve
Convert another temperature
About the Celsius and Fahrenheit scales
Celsius (°C), formerly Centigrade, is the SI temperature scale. It sets 0°C as the freezing point and 100°C as the boiling point of water at standard atmospheric pressure, giving a 100-degree span between the two reference points.
Fahrenheit (°F) is used primarily in the United States and a few Caribbean nations. Its reference points are 32°F (water freezes) and 212°F (water boils) — a span of 180°F for the same interval. One Fahrenheit degree is therefore 5/9 of a Celsius degree.
The two scales intersect at −40°, the only temperature with the same value in both units.
Reference temperatures
| Reference point | °C | °F |
|---|---|---|
| Absolute zero | −273.15 | −459.67 |
| Water freezes | 0 | 32 |
| Room temperature | 20 | 68 |
| Body temperature | 37 | 98.6 |
| Water boils | 100 | 212 |
Frequently asked questions
40°C = 104°F. Using the formula: 40 × 9/5 + 32 = 72 + 32 = 104.
Normal body temperature is about 37°C, which equals 98.6°F.
−40° is the only temperature equal in both scales: −40°C = −40°F.
Multiply by 9/5 (1.8) then add 32. Example: 100°C → 100 × 1.8 + 32 = 212°F.
Subtract 32 then multiply by 5/9. Example: 98.6°F → (98.6 − 32) × 5/9 = 37°C.
Double the Celsius value and add 30 for a rough estimate. Example: 20°C → 20 × 2 + 30 = 70°F (exact: 68°F).