Convert any temperature between Celsius, Fahrenheit, Kelvin, and Rankine. Unlike length or weight converters, temperature is affine (multiply plus add), not linear (multiply only) — the scales have different zero points, not just different unit sizes. The tool handles the offsets correctly for all twelve possible conversion pairs.
The conversion formulas
- °C → °F: F = C × 9/5 + 32
- °F → °C: C = (F − 32) × 5/9
- °C → K: K = C + 273.15
- K → °C: C = K − 273.15
- K → °F: F = (K − 273.15) × 9/5 + 32
- °R = K × 9/5, so Rankine and Kelvin differ only by the 9/5 scale factor
The tool routes everything through Kelvin internally, so there are only four to-Kelvin conversions and four from-Kelvin conversions, and any target-source pair is just a composition of two. This keeps the code small and guarantees consistency: C → F via K gives the same answer as C → F directly.
Example: key reference points
| Condition | Celsius | Fahrenheit | Kelvin | Rankine |
|---|---|---|---|---|
| Absolute zero | −273.15 | −459.67 | 0 | 0 |
| Water freezes | 0 | 32 | 273.15 | 491.67 |
| Body temperature | 37 | 98.6 | 310.15 | 558.27 |
| Water boils | 100 | 212 | 373.15 | 671.67 |
| Hot oven | 200 | 392 | 473.15 | 851.67 |
Example: cooking
A US recipe calls for a 375 °F oven. That’s (375 − 32) × 5/9 = 190.6 °C, which you’d set your European oven to. 180 °C (a common European recipe temperature) is 356 °F. Rough rule of thumb: 350 °F ≈ 180 °C, 400 °F ≈ 200 °C.
Example: weather
25 °C is a pleasant summer day. In Fahrenheit: 25 × 9/5 + 32 = 77 °F. 30 °C is hot: 86 °F. 35 °C is very hot: 95 °F. 40 °C is dangerously hot: 104 °F. 0 °C = 32 °F is the freezing point. −10 °C = 14 °F is cold. −20 °C = −4 °F is very cold.
Example: scientific conversion
Room temperature is about 293.15 K = 20 °C = 68 °F = 527.67 °R. When a physics textbook says “at room temperature,” it usually means this reference. Liquid nitrogen boils at 77.36 K = −195.79 °C = −320.43 °F.
The −40 identity
The one temperature where Celsius and Fahrenheit agree: −40 °C = −40 °F. This comes from setting F = C in the conversion formula: C = 9C/5 + 32, which solves to C = −40. Useful for sanity-testing any temperature converter — the round trip at −40 should be exact regardless of which unit you start with.
What this tool does not do
It doesn’t handle negative Kelvin or negative Rankine meaningfully. The conversion runs, but the warning surfaces. Both are absolute scales — there’s no physical temperature below zero on either.
It doesn’t distinguish different thermodynamic temperatures (dry bulb, wet bulb, dew point, heat index). These are all °C or °F depending on context, but interpreting them correctly needs atmospheric context beyond unit conversion.
It doesn’t handle obsolete scales — Newton, Delisle, Réaumur, Rømer. These exist historically but aren’t in use.
It doesn’t convert temperature differences vs. absolute temperatures. The formulas assume the values are absolute temperatures (where the zero-point offsets matter). For temperature differences — like “the temperature rose by 25 °C” — you’d use the multiplicative factor only (25 × 9/5 = 45 °F rise), without the 32 or 273.15 offset. If you need delta-temp conversion, compute two conversions and subtract.
For the heat side of thermodynamics, the energy converter handles joules, calories, kWh and the rest.