Temperature Converter
Convert between Celsius, Fahrenheit, Kelvin, Rankine, Réaumur, and Centigrade temperature scales.
Quick Reference — 1 unit = ? Fahrenheit (°F)
| Unit | Value |
|---|---|
| Celsius (°C) | 33.8 |
| Fahrenheit (°F) | 1 |
| Kelvin (K) | -457.87 |
| Rankine (°R) | -458.67 |
| Réaumur (°Ré) | 34.25 |
| Centigrade (historical, = °C) | 33.8 |
Formula
C to F: (°C × 9/5) + 32 | F to C: (°F − 32) × 5/9 | K = °C + 273.15 | °R = (°C + 273.15) × 9/5 | °Ré = °C × 4/5
Everyday Uses
Weather abroad
"28°C today" — is that beach weather or sweater weather? (It's 82°F — beach.) Convert forecasts when traveling or chatting across borders.
Oven settings
A US recipe says 350°F, your oven dial is Celsius (177°C, use 180). Convert cooking temperatures so dinner isn't raw or burnt.
Fever readings
A thermometer says 38.5°C — that's 101.3°F. Convert body temperatures when medical info and your thermometer disagree on units.
Science class
Kelvin for physics, Celsius for chemistry, Fahrenheit in the textbook — move between all three including absolute zero context.
Frequently Asked Questions
What are the formulas for converting between Celsius, Fahrenheit, and Kelvin?
Celsius ↔ Fahrenheit: °F = (°C × 9/5) + 32 and °C = (°F − 32) × 5/9. Celsius ↔ Kelvin: K = °C + 273.15 and °C = K − 273.15. Fahrenheit ↔ Kelvin: K = (°F + 459.67) × 5/9. Quick mental trick for C→F: double the Celsius and add 30 (approximate). Example: 20°C → 40 + 30 = 70°F (actual: 68°F). More precise: double and add 32 for a closer estimate.
What are the key temperature reference points to know?
Important benchmarks: −40°C = −40°F (the only point where both scales are equal). 0°C = 32°F (water freezes). 20°C = 68°F (comfortable room temperature). 37°C = 98.6°F (normal body temperature). 100°C = 212°F (water boils at sea level). 180°C = 356°F (typical baking temperature). 233°C = 451°F (flash point of paper — Fahrenheit 451). 1,064°C = 1,947°F (gold melting point). Oven temperatures: 150°C = 300°F (low), 200°C = 390°F (moderate), 230°C = 445°F (high).
What is absolute zero and why does the Kelvin scale start there?
Absolute zero (0 K = −273.15°C = −459.67°F) is the theoretically coldest possible temperature — the point where all thermal motion of atoms stops. The Kelvin scale is an absolute thermodynamic scale with 0 at this lower limit, so temperatures in Kelvin are never negative. Kelvin is used in science and physics because equations for gas laws (PV = nRT), blackbody radiation, and thermodynamics require an absolute scale. 1 K increment = 1°C increment; only the zero point differs.
Why does water boil at 100°C (212°F) but not always at high altitude?
Water boils when vapour pressure equals atmospheric pressure. At sea level (1 atm = 101.325 kPa), the boiling point is 100°C. At altitude, atmospheric pressure is lower, so water boils at a lower temperature: at 2,000 m (6,562 ft), water boils at ~93°C; at 5,000 m (16,404 ft) — base camp Everest — it boils at ~83°C. This is why cooking pasta or boiling eggs takes longer at altitude: lower boiling temperature = slower cooking. A pressure cooker raises boiling point above 100°C by increasing pressure.
Who invented Celsius and Fahrenheit, and which countries use each scale?
Fahrenheit (°F) was invented by Daniel Gabriel Fahrenheit (1724). He set 0°F as the coldest brine mixture he could make, and 96°F as body temperature (later adjusted). Used today in: USA, Cayman Islands, Bahamas, Liberia, and a few others. Celsius (°C, originally "Centigrade") was proposed by Anders Celsius (1742), with 0° at freezing and 100° at boiling. Used almost everywhere else in the world. Kelvin (K) was defined by Lord Kelvin (William Thomson) in 1848 based on thermodynamic principles.
What is the Rankine scale and where is it still used?
Rankine (°R or °Ra) is an absolute thermodynamic scale, like Kelvin, but its degree size matches Fahrenheit rather than Celsius: 0 °R = absolute zero = −459.67°F, and a 1°R change equals a 1°F change. Conversion: °R = °F + 459.67, or °R = (°C + 273.15) × 9/5. It is used mainly in older US engineering disciplines — thermodynamics, aerospace, and steam/gas turbine calculations — where formulas need an absolute scale but engineers still think in Fahrenheit. Water freezes at 491.67°R and boils at 671.64°R.
What is the Réaumur scale and how does it compare to Celsius?
The Réaumur scale (°Ré or °Re) was devised by René Antoine Ferchault de Réaumur in 1730. It sets water's freezing point at 0°Ré and boiling point at 80°Ré (instead of 100), so 1°Ré = 1.25°C. Conversion: °Ré = °C × 4/5, and °C = °Ré × 5/4. It was widely used in parts of Europe (notably France, Germany, and Russia) until the 19th century, when it was gradually replaced by Celsius. Today it survives mainly in some traditional cheese-making and maple syrup production references in France and Quebec.
What is "Centigrade" and is it the same as Celsius?
Centigrade was the original name for the Celsius scale — both divide the interval between water's freezing point (0°) and boiling point (100°) into 100 equal degrees ("centi-grade" literally means "hundred steps"). The scale was renamed Celsius in 1948 by an international weights-and-measures conference to honour its inventor, Anders Celsius, and to avoid confusion with the "grade" (gradian) angular unit. The numbers and formulas are identical — converting Centigrade is the same as converting Celsius.