Temperature Conversion Guide: Celsius, Fahrenheit, and Kelvin

Understanding Temperature Scales

Three temperature scales dominate worldwide usage: Celsius (metric), Fahrenheit (US), and Kelvin (scientific). Here's how they work and how to convert between them.

The Three Scales

Celsius (°C)

The Global Standard

Used by most of the world for daily temperatures:

• Freezing point of water: 0°C


• Boiling point of water: 100°C


• Room temperature: ~20-22°C


• Body temperature: 37°C

Named after Anders Celsius (1742)

Fahrenheit (°F)

Used in the United States

The US standard for weather and cooking:

• Freezing point of water: 32°F


• Boiling point of water: 212°F


• Room temperature: ~68-72°F


• Body temperature: 98.6°F

Named after Daniel Fahrenheit (1724)

Kelvin (K)

The Scientific Scale

Used in science, starts at absolute zero:

• Absolute zero: 0 K (-273.15°C)


• Freezing point of water: 273.15 K


• Boiling point of water: 373.15 K


• Room temperature: ~293-295 K

Note: Kelvin uses no degree symbol (just "K")

Conversion Formulas

Celsius ↔ Fahrenheit

Celsius to Fahrenheit:


°F = (°C × 9/5) + 32

Fahrenheit to Celsius:


°C = (°F - 32) × 5/9

Celsius ↔ Kelvin

Celsius to Kelvin:


K = °C + 273.15

Kelvin to Celsius:


°C = K - 273.15

Fahrenheit ↔ Kelvin

Fahrenheit to Kelvin:


K = (°F - 32) × 5/9 + 273.15

Kelvin to Fahrenheit:


°F = (K - 273.15) × 9/5 + 32

Quick Reference Table

Mental Math Shortcuts

Quick Celsius to Fahrenheit

Double and add 30 (approximate)

20°C → 40 + 30 = 70°F (actual: 68°F)

30°C → 60 + 30 = 90°F (actual: 86°F)

Quick Fahrenheit to Celsius

Subtract 30 and halve (approximate)

70°F → (70-30)/2 = 20°C (actual: 21°C)

90°F → (90-30)/2 = 30°C (actual: 32°C)

Key Points to Remember

0°C = 32°F (freezing)

10°C = 50°F (cool)

20°C = 68°F (room temp)

30°C = 86°F (hot)

Practical Applications

Cooking Temperatures

Common Recipes:

Cookies: 180°C / 350°F

Bread: 200°C / 400°F

Roast: 175°C / 350°F

Weather Interpretation

Celsius Quick Guide:

Below 0°C: Freezing, ice possible

0-10°C: Cold, need coat

10-20°C: Cool, light jacket

20-25°C: Comfortable

25-30°C: Warm

Above 30°C: Hot

Above 40°C: Extreme heat

Body Temperature

Fever Thresholds:

Description	Celsius	Fahrenheit	Kelvin
Absolute zero	-273.15	-459.67	0
Freezing water	0	32	273.15
Cold day	10	50	283
Room temp	20	68	293
Warm day	25	77	298
Body temp	37	98.6	310
Hot day	35	95	308
Boiling water	100	212	373.15
Setting	Celsius	Fahrenheit
Low	120-150	250-300
Medium	160-180	325-350
High	190-220	375-425
Broil	230-260	450-500
Condition	Celsius	Fahrenheit
Normal	36.1-37.2	97-99
Low fever	37.3-38.0	99.1-100.4
Fever	38.1-39.0	100.5-102.2
High fever	Above 39	Above 102




Scientific Applications

Kelvin is essential for:


• Physics calculations


• Chemistry (gas laws)


• Astronomy


• Color temperature (photography)

Color Temperature:


• Candlelight: ~1,800 K


• Sunrise: ~3,000 K


• Daylight: ~5,500 K


• Blue sky: ~10,000 K

Why Different Scales Exist

Fahrenheit (1724): Based on brine freezing and human body temperature

Celsius (1742): Based on water's freezing and boiling points

Kelvin (1848): Based on absolute zero for scientific precision

Convert Temperatures Instantly

Use our unit converter to convert between Celsius, Fahrenheit, and Kelvin instantly. Perfect for cooking, travel, and science.