Instantly convert between Celsius, Fahrenheit, and Kelvin — with oven temperatures, body temperature references and UK weather records.
Enter any temperature in Celsius, Fahrenheit, or Kelvin — the other two values update instantly.
These three formulas cover all conversions between the three major temperature scales.
Multiply the Celsius value by 1.8 (or 9 divided by 5), then add 32. This formula is used every day for cooking, weather forecasting and medicine.
Example: Convert 25°C to Fahrenheit → (25 × 1.8) + 32 = 45 + 32 = 77°F
Subtract 32 from the Fahrenheit value first, then multiply by 5/9 (or divide by 1.8). This is the reverse of the formula above.
Example: Convert 98.6°F to Celsius → (98.6 − 32) × 5/9 = 66.6 × 0.5556 = 37°C
Simply add 273.15 to the Celsius value. Kelvin uses the same scale increments as Celsius but starts at absolute zero, making it essential for scientific calculations.
Example: Water boils at 100°C → 100 + 273.15 = 373.15 K
These benchmarks are essential for everyday use, from cooking to science to medicine.
| Description | Celsius (°C) | Fahrenheit (°F) | Kelvin (K) |
|---|---|---|---|
| Absolute Zero | −273.15 | −459.67 | 0 |
| Coldest UK ever recorded | −27.2 | −16.96 | 245.95 |
| Water freezing point | 0 | 32 | 273.15 |
| Cold winter day (UK) | 2 | 35.6 | 275.15 |
| Celsius = Fahrenheit crossover | −40 | −40 | 233.15 |
| Normal room temperature | 20 | 68 | 293.15 |
| Normal body temperature | 37 | 98.6 | 310.15 |
| Human fever threshold | 38 | 100.4 | 311.15 |
| Hot summer day (UK record) | 40.3 | 104.54 | 313.45 |
| Water boiling point (sea level) | 100 | 212 | 373.15 |
UK coldest: −27.2°C at Braemar, Scotland (January 1982 & January 1995). UK hottest: 40.3°C at Coningsby, Lincolnshire (19 July 2022).
UK recipes frequently use Gas Marks. Here is the complete conversion table for all gas marks used in British baking and cooking.
| Gas Mark | Celsius (°C) | Fahrenheit (°F) | Description |
|---|---|---|---|
| Gas Mark ¼ | 110 | 225 | Very Cool |
| Gas Mark ½ | 130 | 250 | Very Cool |
| Gas Mark 1 | 140 | 275 | Cool / Slow |
| Gas Mark 2 | 150 | 300 | Cool / Slow |
| Gas Mark 3 | 170 | 325 | Warm |
| Gas Mark 4 | 180 | 350 | Moderate |
| Gas Mark 5 | 190 | 375 | Moderately Hot |
| Gas Mark 6 | 200 | 400 | Hot |
| Gas Mark 7 | 220 | 425 | Hot (Roasting) |
| Gas Mark 8 | 230 | 450 | Very Hot |
| Gas Mark 9 | 240 | 475 | Very Hot |
Fan-assisted ovens typically run 20°C cooler. Always check your appliance manual for precise calibration.
Understanding where each scale comes from helps explain why they differ and when each one is appropriate to use.
Proposed by Swedish astronomer Anders Celsius in 1742, the original scale was actually inverted (0 = boiling, 100 = freezing). It was reversed after his death by Carl Linnaeus. Today it is the international standard for everyday temperature measurement in virtually every country except the United States.
Developed by German physicist Daniel Gabriel Fahrenheit in 1724. He set 0°F as the freezing point of a brine solution (ice, water, and ammonium chloride) and 96°F as approximate human body temperature. His scale was later refined so that water freezes at exactly 32°F and boils at 212°F. The United States, the Cayman Islands, and a few other territories still use Fahrenheit as the primary scale.
Named after Belfast-born physicist William Thomson (Lord Kelvin), 1st Baron Kelvin, who proposed an absolute temperature scale in 1848. Kelvin uses the same degree size as Celsius but begins at absolute zero (−273.15°C), the theoretical point where all thermal motion stops. Kelvin is used universally in scientific and engineering contexts.
Proposed by Scottish engineer William Rankine in 1859, the Rankine scale is an absolute scale based on Fahrenheit degrees. Absolute zero is 0°R, and water freezes at 491.67°R. It is occasionally used in some US engineering applications but is largely obsolete outside of that context.
How UK temperatures relate to real-world events and seasonal expectations.
The Met Office uses Celsius for all official UK weather forecasts. Fahrenheit temperatures may still appear in some legacy contexts or for American visitors.
A quick mental approximation: double the Celsius temperature and add 30. For example, 20°C → (20 × 2) + 30 = 70°F (actual answer is 68°F). This is accurate to within a few degrees for everyday temperatures. For a more precise answer, use the exact formula: °F = (°C × 9/5) + 32.
Normal adult body temperature is 37°C (98.6°F). This can naturally vary slightly throughout the day. A temperature of 38°C (100.4°F) or above is generally considered a fever. Hypothermia is diagnosed when core body temperature falls below 35°C (95°F).
The two scales meet at exactly −40 degrees: −40°C = −40°F. This is the only temperature that is identical on both scales. You can verify this using the formula: −40°C × 9/5 + 32 = −72 + 32 = −40°F. This crossover point is useful to remember as a mental check.
Absolute zero is −273.15°C (0 K, −459.67°F). It is the lowest theoretically possible temperature, where all molecular thermal motion ceases. Scientists have cooled materials to within fractions of a nano-Kelvin of absolute zero in laboratory conditions, but the third law of thermodynamics states it can never actually be reached.
The UK officially adopted Celsius as part of metrication during the 1960s and 1970s. The USA never fully metricated and retained Fahrenheit for everyday use. Fahrenheit was developed in the early 18th century and became the standard in British colonies, but the UK later adopted the metric Celsius system for scientific coherence with Europe and the rest of the world.
First, find the Celsius equivalent for the gas mark (e.g., Gas Mark 6 = 200°C), then reduce by 20°C for a fan-assisted oven (200 − 20 = 180°C). Fan ovens circulate heat more efficiently, so they cook faster and at lower temperatures. Always check your oven manual, as some fan ovens require only a 10°C reduction.