How do you convert Celsius to Fahrenheit?

To convert Celsius to Fahrenheit, use the formula: °F = (°C × 9/5) + 32. For example, 20°C = (20 × 9/5) + 32 = 68°F. Quick method: multiply by 2 and add 30 for an approximate conversion (20°C × 2 + 30 = 70°F, close to 68°F).

How do you convert Fahrenheit to Celsius?

To convert Fahrenheit to Celsius, use the formula: °C = (°F - 32) × 5/9. For example, 68°F = (68 - 32) × 5/9 = 20°C. Quick method: subtract 30 and divide by 2 for an approximate conversion (68°F - 30) / 2 = 19°C, close to 20°C).

What is the difference between Celsius and Kelvin?

Kelvin and Celsius use the same scale size (1°C = 1K), but Kelvin starts at absolute zero (-273.15°C). To convert: K = °C + 273.15. For example, 0°C = 273.15K, and 100°C = 373.15K. Kelvin is used in scientific applications and never uses the degree symbol (just K, not °K).

Which countries use Fahrenheit vs Celsius?

Celsius is used by most countries worldwide (195+ countries). Fahrenheit is primarily used in the United States, and to a lesser extent in the Bahamas, Belize, Cayman Islands, and Palau. The US is the only major industrialized country still using Fahrenheit for everyday temperatures. Scientists worldwide use Celsius or Kelvin.

Temperature Converter - Celsius, Fahrenheit, Kelvin & Rankine | AICalculator

Understanding Temperature Scales

Temperature is a measure of thermal energy, and different scales have been developed throughout history to measure it. Understanding how to convert between these scales is essential for international communication, scientific work, cooking, and everyday life.

The Four Temperature Scales

🌡️ Celsius (°C)

Used by: Most of the world (195+ countries)

• Water freezes at 0°C
• Water boils at 100°C
• Based on water's properties
• Named after Anders Celsius

🌡️ Fahrenheit (°F)

Used by: United States, some Caribbean nations

• Water freezes at 32°F
• Water boils at 212°F
• 180 degrees between freeze/boil
• Named after Daniel Fahrenheit

🌡️ Kelvin (K)

Used by: Scientists worldwide

• Starts at absolute zero (0K)
• Water freezes at 273.15K
• Water boils at 373.15K
• SI unit for temperature

🌡️ Rankine (°R)

Used by: Some US engineering applications

• Starts at absolute zero (0°R)
• Water freezes at 491.67°R
• Water boils at 671.67°R
• Rarely used today

Conversion Formulas

From Celsius:

• To Fahrenheit: °F = (°C × 9/5) + 32
• To Kelvin: K = °C + 273.15
• To Rankine: °R = (°C + 273.15) × 9/5

From Fahrenheit:

• To Celsius: °C = (°F - 32) × 5/9
• To Kelvin: K = (°F + 459.67) × 5/9
• To Rankine: °R = °F + 459.67

Quick Mental Conversions

Celsius to Fahrenheit (Approximate)

Method: Multiply by 2 and add 30

Example: 20°C → (20 × 2) + 30 = 70°F (actual: 68°F)

Fahrenheit to Celsius (Approximate)

Method: Subtract 30 and divide by 2

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

Common Temperature References

Description	°C	°F	K
Absolute Zero	-273.15	-459.67	0
Dry Ice Sublimes	-78.5	-109.3	194.65
Water Freezes	0	32	273.15
Room Temperature	20-22	68-72	293-295
Human Body Temp	37	98.6	310.15
Water Boils (sea level)	100	212	373.15
Oven Baking	180-220	350-425	453-493

Historical Context

Fahrenheit (1724): Daniel Fahrenheit created his scale using three reference points: the coldest temperature he could create with ice and salt (0°F), the freezing point of water (32°F), and human body temperature (originally 96°F, later adjusted to 98.6°F).

Celsius (1742): Anders Celsius proposed a scale with 0° as water's boiling point and 100° as its freezing point. This was later inverted to the current system where 0°C is freezing and 100°C is boiling.

Kelvin (1848): William Thomson (Lord Kelvin) proposed an absolute temperature scale starting at absolute zero, the theoretical lowest possible temperature where molecular motion stops.

Practical Applications

Cooking: Recipe conversions between Celsius and Fahrenheit ovens
Weather: Understanding forecasts when traveling internationally
Science: Laboratory work requires Kelvin for absolute measurements
Medicine: Body temperature monitoring (37°C = 98.6°F = fever threshold)
HVAC: Setting thermostats in different regions
Manufacturing: Process control in international operations