How to Convert Temperature Units

Three temperature scales are in common use:

• Celsius (°C) — the international standard for everyday use; water freezes at 0°C, boils at 100°C
• Fahrenheit (°F) — still used in the United States for weather, cooking, and body temperature
• Kelvin (K) — the SI base unit for thermodynamics; starts at absolute zero (no degree symbol)

Conversion Formulas

Celsius ↔ Fahrenheit

°F = (°C × 9/5) + 32
°C = (°F − 32) × 5/9

Example: 37°C (normal body temperature) → (37 × 9/5) + 32 = 66.6 + 32 = 98.6°F

Celsius ↔ Kelvin

K  = °C + 273.15
°C = K − 273.15

Example: 0°C (freezing point) → 0 + 273.15 = 273.15 K

Fahrenheit ↔ Kelvin

K  = (°F − 32) × 5/9 + 273.15
°F = (K − 273.15) × 9/5 + 32

Quick Reference Table

Description	°C	°F	K
Absolute zero	−273.15	−459.67	0
Freezing point of water	0	32	273.15
Room temperature	20–22	68–72	293–295
Normal body temperature	37	98.6	310.15
Boiling point of water	100	212	373.15
Oven — moderate	180	356	453
Oven — hot	220	428	493

Common Conversion Points to Memorise

A few anchor points make rough mental conversions easy:

• 0°C = 32°F (freezing)
• 20°C ≈ 68°F (mild room temp)
• 37°C = 98.6°F (body temp)
• 100°C = 212°F (boiling)

For a rough Celsius-to-Fahrenheit estimate: double the Celsius value and add 30. This gives ±2°F accuracy across 0–40°C.

Why Three Scales?

• Kelvin was defined for thermodynamic calculations where negative temperatures are meaningless. Gas laws (PV = nRT) use Kelvin.
• Celsius was designed so 0° and 100° align with water phase changes — intuitive for science and daily life.
• Fahrenheit was calibrated using brine (0°F) and body temperature (originally 96°F before revision). It remains in everyday use in the US.

Use the Temperature Converter to convert any value between all three scales instantly.