Celsius to Fahrenheit Converter

How to Convert Celsius to Fahrenheit

The formula to convert Celsius (C) to Fahrenheit (F) is:

F = (C × 9/5) + 32

This formula works by first scaling the Celsius value to match the size of a Fahrenheit degree (there are 180 Fahrenheit degrees between freezing and boiling, versus 100 Celsius degrees, giving a ratio of 9/5 = 1.8), then shifting the result by 32 to account for the different zero points (water freezes at 0°C but 32°F).

Worked Example

Convert 100°C (the boiling point of water at sea level) to Fahrenheit:

1. Multiply by 9/5: 100 × 9/5 = 100 × 1.8 = 180
2. Add 32: 180 + 32 = 212°F

So 100°C = 212°F. This is one of the most useful reference points to memorise.

How to Convert Fahrenheit to Celsius

The reverse formula is:

C = (F - 32) × 5/9

For example, to convert 98.6°F (normal body temperature) to Celsius:

1. Subtract 32: 98.6 - 32 = 66.6
2. Multiply by 5/9: 66.6 × 5/9 = 66.6 × 0.5556 = 37°C

Quick Mental Estimate

For a rough Celsius to Fahrenheit estimate in your head, double the Celsius temperature and add 30. For example, 20°C gives approximately 20 × 2 + 30 = 70°F (the exact answer is 68°F). This is slightly off but useful when precision is not needed.

In the other direction, subtract 30 from Fahrenheit and divide by 2 to estimate Celsius. For example, 80°F gives approximately (80 - 30) / 2 = 25°C (the exact answer is 26.7°C).

The Celsius and Fahrenheit Scales

The Celsius scale (formerly called centigrade) was developed in the 18th century and is defined so that water freezes at 0°C and boils at 100°C at standard atmospheric pressure. It is the scale used in most countries worldwide and in all scientific work.

The Fahrenheit scale was developed by Daniel Gabriel Fahrenheit in the early 1700s. It sets the freezing point of water at 32°F and the boiling point at 212°F. It is still used in everyday life in the United States and a small number of other countries. New Zealand uses Celsius for all official and everyday temperature measurements.

The Kelvin scale is the SI (metric) absolute temperature scale. Zero Kelvin (absolute zero) is the coldest possible temperature, equal to -273.15°C or -459.67°F. Kelvin values are used in scientific calculations such as gas laws and thermodynamics. To convert Celsius to Kelvin, add 273.15.

Related Calculators

• Essential Calculators: the full converter and utility hub.
• Unit Converter: convert between many common units of measurement.
• Area Conversion Calculator: convert between square metres, hectares, acres, and more.
• Basal Metabolic Rate Calculator: body temperature is key to understanding metabolic rate.
• Appliance Running Cost Calculator: heating and cooling costs depend on temperature settings.

Sources and method: International Bureau of Weights and Measures (BIPM), SI Brochure, 9th edition (2019). The Celsius to Fahrenheit formula F = (C × 9/5) + 32 is standardised by international agreement. The Kelvin scale offset of 273.15 is defined in the 2019 revision of the SI.

This converter applies the standard, exact Celsius to Fahrenheit conversion formula. Boiling and freezing points quoted are at standard atmospheric pressure (101.325 kPa). Actual boiling point varies slightly with altitude and atmospheric conditions.