How to Convert Celsius to Fahrenheit Online — Free Temperature Converter

The formulas

Celsius → Fahrenheit: °F = (°C × 9/5) + 32

Fahrenheit → Celsius: °C = (°F − 32) × 5/9

Celsius → Kelvin: K = °C + 273.15

The temperature converter runs all three simultaneously — type in any field, see all others update.

Reference points everyone should know

What	°C	°F	K
Absolute zero	−273.15	−459.67	0
Water freezes	0	32	273.15
Room temperature	20-22	68-72	~295
Human body	37	98.6	310.15
Oven, baking bread	200	400	473.15
Water boils (sea level)	100	212	373.15
−40 (the cross-over)	−40	−40	233.15

The mental-math shortcut

If you don't have a calculator: double the Celsius and add 30 gets you within 3-5°F for typical weather temperatures. 20°C ≈ 70°F (actual 68), 30°C ≈ 90°F (actual 86). Not accurate for cooking or medical purposes, but good enough for "is it warm outside?"

Why the awkward 5/9 factor?

Fahrenheit's scale was set so that 0°F was the coldest temperature Fahrenheit could achieve in his lab (brine + ice), and 100°F was roughly body temperature. Celsius later set 0 = water freezes and 100 = water boils. Neither anchor is "natural" — they just happen to differ by a factor of 9/5 between water's freeze/boil points.

Altitude affects boiling, not freezing

At sea level, water boils at 100°C / 212°F. At 2,500 m (Denver) it boils at roughly 92°C / 198°F. That's why recipes say "adjust at altitude" — lower boiling temperature means longer cooking times for starches and proteins. The temperature converter doesn't correct for altitude; use the raw conversion and then add altitude context separately.

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