How it works
Why three scales still coexist
A reliable temperature converter is one of the most-used tools on any calculadora site, because daily life in the UK runs on three temperature scales at once: °C for weather and cooking, °F for American recipes and older thermometers, and K in physics, chemistry and astronomy. Each scale picks a different reference point — the freezing point of water (Celsius), a brine solution (Fahrenheit) or absolute zero (Kelvin) — so the conversion formulas are not just "multiply and add" but carry real physical meaning.
The three exact formulas
- Celsius → Fahrenheit: °F = (°C × 9/5) + 32
- Fahrenheit → Celsius: °C = (°F − 32) × 5/9
- Celsius → Kelvin: K = °C + 273.15
- Kelvin → Celsius: °C = K − 273.15
- Fahrenheit → Kelvin: K = (°F − 32) × 5/9 + 273.15
Three worked examples
1. UK weather — "it's 28 °C today"
28 × 9/5 + 32 = 50.4 + 32 = 82.4 °F. American visitors usually expect "hot" to start around 85 °F, so 28 °C is "warm but pleasant" on both sides of the Atlantic.
2. American recipe — bake at 375 °F
(375 − 32) × 5/9 = 343 × 5/9 ≈ 190 °C — roughly gas mark 5. For fan ovens, drop 20 °C → 170 °C fan.
3. Physics homework — what is 0 K in °C?
0 K − 273.15 = −273.15 °C. This is absolute zero, the lowest possible temperature where molecular motion stops. The coldest lab experiments have reached ~0.000 000 000 1 K.
Oven temperature cheat-sheet
UK recipes often list gas marks but your oven shows °C; American recipes use °F. Keep this table near the cooker.
- Gas mark ¼ ≈ 110 °C ≈ 225 °F — slow simmer, meringues
- Gas mark 2 ≈ 150 °C ≈ 300 °F — slow roasts, stews
- Gas mark 4 ≈ 180 °C ≈ 350 °F — cakes, most baking
- Gas mark 6 ≈ 200 °C ≈ 400 °F — roasts, pastry
- Gas mark 8 ≈ 230 °C ≈ 450 °F — pizza, searing
Kelvin and absolute zero
Kelvin starts at the coldest theoretically possible temperature (absolute zero, −273.15 °C) and uses the same step size as Celsius. That makes it the scale of choice in physics, where many laws (gas law, Stefan–Boltzmann, Planck distribution) only work with absolute temperature.
Notice we say "290 K" not "290 °K" — the degree symbol was officially dropped in 1967.
Works well with
- **Oven temperature converter** — quick gas mark ↔ °C ↔ °F.
- **Length converter** — handle inches and cm in the same recipe.
- **Recipe scaler** — scale quantities after you convert temperatures.
- **Grams to cups** — pairs with temperature for full recipe localisation.
How we check the formulas
Temperature conversions are fixed by the International System of Units (BIPM SI) and the Kelvin was redefined in 2019 using the Boltzmann constant. We reference the BIPM, NIST and the UK Met Office. See our editorial policy and corrections policy. Every conversion runs client-side — nothing is stored.