Temperature Converter (°C / °F / K)
Convert temperatures between Celsius, Fahrenheit and Kelvin. Unlike other units, temperature scales have different zero points, so these conversions use formulas rather than simple multiplication — all shown below.
How to use this calculator
- Enter the temperature value.
- Select which scale it's in.
- Press Convert to see it in all three scales at once.
Formula used
Celsius and Fahrenheit cross at −40° — the only temperature where both scales read the same number. Kelvin starts at absolute zero (−273.15 °C), the coldest temperature physically possible.
Example calculation
Convert 37 °C to Fahrenheit: 37 × 9/5 + 32 = 66.6 + 32 = 98.6 °F — normal body temperature. In Kelvin: 37 + 273.15 = 310.15 K.
Why temperature conversion needs a formula
Length and weight units share a zero point, so converting is pure multiplication. Temperature scales don't: 0 °C is water's freezing point, 0 °F was the coldest brine mixture Fahrenheit could make, and 0 K is absolute zero. Converting therefore needs both a scale factor (9/5) and an offset (+32).
Handy approximations: to go °C → °F in your head, double it and add 30 (exact: ×1.8 + 32). Room temperature is ~20 °C / 68 °F; a hot day is 35 °C / 95 °F.
Why use this calculator?
- Instant three-way conversion for weather, cooking, science and travel.
- Catches impossible inputs below absolute zero.
- Reference points included so the numbers mean something.
Frequently asked questions
What is the formula for Celsius to Fahrenheit?
°F = °C × 9/5 + 32. Quick estimate: double the Celsius and add 30 — for 20 °C that gives 70 °F vs the exact 68 °F.
What temperature is the same in Celsius and Fahrenheit?
−40°. Set C = C×9/5+32 and solve: C = −40. It's the crossing point of the two scales.
Why does science use Kelvin?
Kelvin starts at absolute zero, so it has no negative values and doubling the kelvin value genuinely doubles the thermal energy — which makes gas laws and thermodynamic equations work cleanly.