Free Temperature Converter
Convert temperature units instantly — Celsius, Fahrenheit, Kelvin, and Rankine. Type into any field and all others update. Free, symmetrical, no sign-up.
Exact Conversion Formula & Multipliers
Unlike most conversions on this site, temperature scales are affine, not simply multiplicative: °F = (°C × 9/5) + 32, K = °C + 273.15, and °R (Rankine) = °F + 459.67. The added constants (32, 273.15, 459.67) matter because they shift the zero point — 0°C is not 'zero times' anything in Fahrenheit, it's 32°F, which is why temperature conversions can't be reduced to a single multiplier the way length or weight can.
Practical Real-World Scenarios
- Cooking: oven temperatures are set in Fahrenheit in the US and Celsius almost everywhere else, so following a recipe from the 'wrong' region means converting every temperature it mentions.
- Weather and travel: a forecast of '30 degrees' means something completely different — dangerously cold versus warm — depending on whether it's Celsius or Fahrenheit.
- Science and engineering: Kelvin is the SI base unit for thermodynamic calculations, since it starts at absolute zero, making it the required scale for physics and chemistry formulas.
Historical & Technical Background
Daniel Gabriel Fahrenheit proposed his scale in 1724, originally anchoring it to a brine mixture's freezing point and (approximately) human body temperature. Anders Celsius introduced his centigrade scale in 1742, originally inverted (0 as boiling, 100 as freezing) before being flipped to today's convention. Kelvin, introduced by William Thomson (Lord Kelvin) in 1848, added the crucial idea of absolute zero — the point at which molecular motion theoretically stops — giving science a scale with no negative values.
Precision & Accuracy Statement
Conversion factors use the exact defined values given in NIST Special Publication 811 and the BIPM SI Brochure wherever such a definition exists (for example 1 lb = 0.45359237 kg, 1 in = 2.54 cm, 1 US gal = 3.785411784 L, g₀ = 9.80665 m/s²); derived factors are computed from those definitions rather than copied as rounded figures. Results are calculated in double-precision floating point and shown to 10 significant digits, so the last digit can differ by one unit of rounding. The rounded figures in the text and tables above are for reading convenience.
How This Converter Works
Temperature scales differ in their zero points and intervals. Celsius and Fahrenheit are the most common everyday scales, while Kelvin is essential for scientific work. Our symmetrical converter updates all four scales simultaneously — type in any field.
Common Conversions
| Celsius (°C) | Fahrenheit (°F) | Kelvin (K) | Context |
|---|---|---|---|
| -40°C | -40°F | 233.15 K | Parity point — both scales are equal |
| 0°C | 32°F | 273.15 K | Freezing point of water |
| 20°C | 68°F | 293.15 K | Standard room temperature |
| 37°C | 98.6°F | 310.15 K | Normal human body temperature |
| 100°C | 212°F | 373.15 K | Boiling point of water |
| 180°C | 356°F | 453.15 K | Standard oven baking temperature |