Celsius to Fahrenheit: Quick Reference + Formula

The Formula — Both Directions

Celsius to Fahrenheit: °F = (°C × 1.8) + 32. Example: 20°C → (20 × 1.8) + 32 = 36 + 32 = 68°F.

Fahrenheit to Celsius: °C = (°F − 32) ÷ 1.8. Example: 98.6°F → (98.6 − 32) ÷ 1.8 = 66.6 ÷ 1.8 = 37°C.

The 1.8 factor comes from the ratio of the two scales' degree sizes. A Fahrenheit degree is exactly 5/9 the size of a Celsius degree — meaning 1°C of temperature change equals 1.8°F of change.

Key Anchor Points to Memorize

Rather than using the formula every time, memorizing a handful of anchor points lets you estimate any temperature quickly.

• −40°C = −40°F (the only point where both scales meet)
• 0°C = 32°F (water freezes)
• 10°C = 50°F (cool autumn day)
• 20°C = 68°F (comfortable room temperature)
• 25°C = 77°F (warm summer day)
• 30°C = 86°F (hot day)
• 37°C = 98.6°F (normal human body temperature)
• 40°C = 104°F (dangerous fever / very hot day)
• 100°C = 212°F (water boils at sea level)

Weather Reference Table

Common weather temperatures in both scales.

• −10°C = 14°F (freezing, heavy winter)
• −5°C = 23°F (below freezing, icy roads)
• 0°C = 32°F (freezing point)
• 5°C = 41°F (cold, coat required)
• 10°C = 50°F (cool, light jacket)
• 15°C = 59°F (mild, spring/autumn)
• 20°C = 68°F (pleasant, warm)
• 25°C = 77°F (warm, summer)
• 30°C = 86°F (hot)
• 35°C = 95°F (very hot)
• 40°C = 104°F (heat wave conditions)

Why Does the US Use Fahrenheit?

Daniel Gabriel Fahrenheit established his scale in 1724, calibrating 0°F to the coldest temperature he could reliably reproduce (a brine and ice mixture) and 96°F to human body temperature. The scale was refined later — body temperature ended up at 98.6°F on the adjusted scale.

Celsius (originally "centigrade") was proposed by Anders Celsius in 1742 and used water's freezing and boiling points as its anchors. Most of the world adopted Celsius when metrication happened in the 19th and 20th centuries. The United States kept Fahrenheit because consumer adoption never happened — the same political and economic inertia that kept miles and pounds also kept Fahrenheit.

From a scientific standpoint, neither scale is used for serious work — both have been replaced by Kelvin (which starts at absolute zero, −273.15°C). But for daily weather forecasting and household use, Celsius is the clear international standard.

Conclusion

Celsius to Fahrenheit: multiply by 1.8 and add 32. Fahrenheit to Celsius: subtract 32 and divide by 1.8. The five most useful anchors: 0°C = 32°F (freezing), 20°C = 68°F (room temp), 37°C = 98.6°F (body temp), 100°C = 212°F (boiling), and −40 where both scales meet.