Why is body temperature 37 °C but 98.6 °F?

They are the same temperature written on two scales: 37 × 1.8 + 32 = 98.6.

At what temperature are Celsius and Fahrenheit equal?

At −40, where both scales read the same number.

How to Convert Celsius to Fahrenheit (and Back)

Two exact formulas, a mental shortcut that gets you close, and a table of the temperatures people look up most.

By Editorial Team · Updated September 19, 2026 · 1 min read

Celsius and Fahrenheit use different zero points and different degree sizes, so converting between them needs both a multiplication and an addition or subtraction.

The formulas

Fahrenheit = Celsius × 9 ÷ 5 + 32
Celsius    = (Fahrenheit − 32) × 5 ÷ 9

A Celsius degree is 1.8 times as large as a Fahrenheit degree (9 ÷ 5), and freezing water is 0 °C but 32 °F. That is why the formula multiplies first and adds 32.

Example: Celsius to Fahrenheit

Convert 20 °C. 20 × 9 ÷ 5 = 36, and 36 + 32 = 68 °F.

Example: Fahrenheit to Celsius

Convert 77 °F. 77 − 32 = 45, and 45 × 5 ÷ 9 = 25 °C.

A mental shortcut

To estimate Celsius to Fahrenheit, double the number and add 30. For 20 °C that gives 70 °F, close to the exact 68. To go back, subtract 30 and halve: 70 °F gives 20 °C. The shortcut drifts at extremes, so use the formula when accuracy matters.

Common temperatures

Situation	°C	°F
Water freezes	0	32
Cool room	18	64.4
Comfortable room	20	68
Normal body temperature	37	98.6
Water boils at sea level	100	212
Moderate oven	180	356

The two scales agree at −40: −40 °C is exactly −40 °F.

Kelvin

Kelvin has the same degree size as Celsius but starts at absolute zero: K = °C + 273.15. Nothing can be colder than 0 K, which is −273.15 °C.

Common mistakes

Adding 32 before multiplying.
Using 5 ÷ 9 in the wrong direction.
Converting a temperature difference. A change of 10 °C is a change of 18 °F, with no +32.

The temperature converter handles Celsius, Fahrenheit and Kelvin, and rejects values below absolute zero.

Try it yourself

Convert 30 °C to Fahrenheit.
Convert 50 °F to Celsius.
Convert 5 °C to Fahrenheit.

Answers: (1) 86 °F (30 × 1.8 + 32); (2) 10 °C ((50 − 32) × 5 ÷ 9); (3) 41 °F.

Frequently asked questions

What is 25 degrees Celsius in Fahrenheit?: 25 × 9 ÷ 5 + 32 = 77 °F.
Why is body temperature 37 °C but 98.6 °F?: They are the same temperature written on two scales: 37 × 1.8 + 32 = 98.6.
At what temperature are Celsius and Fahrenheit equal?: At −40, where both scales read the same number.

About the author

Editorial Team. The Editorial Team writes, checks and maintains every tool and guide on this site. The calculation logic behind the calculators is covered by automated tests, examples are worked out and re-checked before publishing, and pages are updated when we find a mistake or a rule changes. Corrections are welcome through the contact page.

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