Temperature Conversion Chart: Celsius, Fahrenheit, Kelvin

The Three Temperature Scales Explained

Celsius (°C)

The Celsius scale, also known as centigrade, is the most widely used temperature scale in the world. It was developed by Swedish astronomer Anders Celsius in 1742. The scale sets the freezing point of water at 0°C and the boiling point at 100°C (at standard atmospheric pressure, sea level). Celsius is the standard temperature unit in the metric system and is used in nearly every country for everyday and scientific purposes.

Fahrenheit (°F)

The Fahrenheit scale was created by German physicist Daniel Gabriel Fahrenheit in 1724. He set 0°F at the temperature of a freezing mixture of water, ice, and ammonium chloride, and 96°F at approximate human body temperature (later refined to 98.6°F). On this scale, water freezes at 32°F and boils at 212°F. The Fahrenheit scale is primarily used in the United States, its territories, and a few other nations for everyday temperature readings.

Kelvin (K)

The Kelvin scale is the primary temperature unit in the physical sciences. Named after William Thomson, 1st Baron Kelvin, it is an absolute temperature scale where 0 K represents absolute zero — the theoretical temperature at which all thermal motion ceases. Unlike Celsius and Fahrenheit, Kelvin does not use the degree symbol (°). The Kelvin scale uses the same increment size as Celsius, so a change of 1 K equals a change of 1°C. Water freezes at 273.15 K and boils at 373.15 K.

Conversion Formulas

Celsius to Fahrenheit

°F = (°C × 9/5) + 32 or °F = (°C × 1.8) + 32

Example: 25°C = (25 × 1.8) + 32 = 45 + 32 = 77°F

Fahrenheit to Celsius

°C = (°F − 32) × 5/9 or °C = (°F − 32) ÷ 1.8

Example: 98.6°F = (98.6 − 32) ÷ 1.8 = 66.6 ÷ 1.8 = 37°C

Celsius to Kelvin

K = °C + 273.15

Example: 100°C = 100 + 273.15 = 373.15 K

Kelvin to Celsius

°C = K − 273.15

Example: 300 K = 300 − 273.15 = 26.85°C

Fahrenheit to Kelvin

K = (°F − 32) × 5/9 + 273.15

Example: 212°F = (212 − 32) × 5/9 + 273.15 = 100 + 273.15 = 373.15 K

Kelvin to Fahrenheit

°F = (K − 273.15) × 9/5 + 32

Example: 300 K = (300 − 273.15) × 1.8 + 32 = 26.85 × 1.8 + 32 = 48.33 + 32 = 80.33°F

Comprehensive Temperature Conversion Chart

Quick Reference for Everyday Temperatures

For quick mental reference, here are the most commonly encountered temperatures in daily life, shown in all three scales:

Weather Temperatures

Cooking Temperatures

Understanding Absolute Zero

Absolute zero (0 K, −273.15°C, −459.67°F) is the lowest theoretically possible temperature. At this point, atoms and molecules have minimal vibrational motion, and entropy reaches its minimum value. While absolute zero has never been achieved in practice, scientists have come extremely close — within billionths of a degree — in laboratory settings using laser cooling and magnetic evaporative cooling techniques.

Understanding absolute zero is crucial in physics and chemistry because many physical laws are defined relative to it. The ideal gas law, thermodynamic equations, and quantum mechanical models all use absolute temperature (Kelvin) for their calculations.

The Rankine Scale: A Fourth Option

Less commonly encountered is the Rankine scale, which is to Fahrenheit what Kelvin is to Celsius. Rankine uses the Fahrenheit increment but starts at absolute zero. The conversion is: °R = °F + 459.67. So water freezes at 491.67°R and boils at 671.67°R. The Rankine scale is occasionally used in engineering thermodynamics in the United States.

Mental Math Shortcuts

Celsius to Fahrenheit (Quick Estimate)

Double the Celsius value and add 30: °F ≈ (°C × 2) + 30. For 20°C: (20 × 2) + 30 = 70°F (exact: 68°F). This works well for temperatures between −10°C and 30°C.

Fahrenheit to Celsius (Quick Estimate)

Subtract 30 from Fahrenheit and divide by 2: °C ≈ (°F − 30) ÷ 2. For 80°F: (80 − 30) ÷ 2 = 25°C (exact: 26.7°C).

When to Use Each Scale

• Celsius: Everyday weather, cooking, and general temperature measurements in most countries. Also used in many scientific contexts alongside Kelvin.
• Fahrenheit: Everyday weather and cooking in the United States and a few other territories. Some engineering fields in the US also use Fahrenheit.
• Kelvin: Scientific research, physics, chemistry, thermodynamics, and any context requiring absolute temperature. Used universally in the scientific community.
• Rankine: Engineering thermodynamics in the United States, particularly in aerospace and mechanical engineering.

Temperature Conversion Tips

1. Remember key anchor points: 0°C = 32°F (freezing), 100°C = 212°F (boiling), −40°C = −40°F (equal point), and 0 K = −273.15°C (absolute zero).
2. Check your formula direction: A common error is using the wrong formula. Celsius to Fahrenheit multiplies first, then adds. Fahrenheit to Celsius subtracts first, then multiplies.
3. Watch for negative numbers: When converting temperatures below freezing, pay attention to signs. For example, −10°C = (−10 × 1.8) + 32 = −18 + 32 = 14°F.
4. Kelvin never goes negative: Since Kelvin starts at absolute zero, there are no negative Kelvin temperatures. If your calculation gives a negative Kelvin value, you made an error.
5. Use an online converter for precision: For scientific or technical work, use our Universal Unit Converter to avoid rounding errors.