To convert Celsius to Fahrenheit: multiply by 9/5 then add 32. To convert Fahrenheit to Celsius: subtract 32 then multiply by 5/9. Example: 100°C = 212°F; 72°F = 22.2°C. To convert to Kelvin, add 273.15 to the Celsius value.
How to use this converter
Type a temperature in the input field, choose the scale you are converting from, then choose the target scale. The result updates instantly. Quick conversion buttons at the top jump to the most common pairs. All five scales are supported: Celsius, Fahrenheit, Kelvin, Rankine, and Réaumur. All calculations run locally in your browser.
The five temperature scales
Five temperature scales are in regular or historical use. Three are relevant to everyday life; two are specialist or historical.
| Scale | Symbol | Water freezes | Water boils | Use |
|---|---|---|---|---|
| Celsius | °C | 0°C | 100°C | Standard in almost every country; everyday use, science, medicine |
| Fahrenheit | °F | 32°F | 212°F | United States: weather, cooking, body temperature |
| Kelvin | K | 273.15 K | 373.15 K | Science and engineering worldwide; no degree symbol used |
| Rankine | °R | 491.67°R | 671.67°R | US thermodynamics and aerospace engineering |
| Réaumur | °Ré | 0°Ré | 80°Ré | Historical; some traditional European food production |
Kelvin has no degree symbol because it is an absolute scale with a physically meaningful zero point. Saying "300 degrees Kelvin" is technically incorrect; the proper form is "300 kelvin" or "300 K." Rankine is the Fahrenheit equivalent of Kelvin: same degree size as Fahrenheit, but starting from absolute zero.
Celsius and Fahrenheit in depth
The Celsius-Fahrenheit conversion is the most common temperature conversion in everyday life. The formula has two parts because the two scales differ in both their zero point and their degree size.
Celsius to Fahrenheit
Multiply by 9/5 (which scales the degree size), then add 32 (which accounts for the offset between the zero points).
$$F = C \times \frac{9}{5} + 32$$
Examples: 0°C = 32°F, 20°C = 68°F, 37°C = 98.6°F, 100°C = 212°F.
Quick mental estimate: double the Celsius value and add 30. This gives 0°C ≈ 30°F (actual: 32°F) and 20°C ≈ 70°F (actual: 68°F). The estimate is off by a couple of degrees but useful for quick comparisons.
Fahrenheit to Celsius
Subtract 32 first (remove the zero-point offset), then multiply by 5/9 (scale back to Celsius degree size).
$$C = (F - 32) \times \frac{5}{9}$$
Examples: 32°F = 0°C, 72°F = 22.2°C, 98.6°F = 37°C, 212°F = 100°C.
Celsius to Kelvin
Celsius and Kelvin use the same degree size, so you only need to shift the zero point.
$$K = C + 273.15$$
Examples: 0°C = 273.15 K, 25°C = 298.15 K, 100°C = 373.15 K.
Key reference points
These are the most useful fixed points across all five scales.
| Point | °C | °F | K | °R | °Ré |
|---|---|---|---|---|---|
| Absolute zero | -273.15 | -459.67 | 0 | 0 | -218.52 |
| Liquid nitrogen | -196 | -321 | 77.15 | 138.87 | -156.8 |
| Freezer temperature | -18 | 0 | 255.15 | 459.27 | -14.4 |
| Water freezes | 0 | 32 | 273.15 | 491.67 | 0 |
| Cool room | 18 | 64.4 | 291.15 | 524.07 | 14.4 |
| Room temperature | 20 | 68 | 293.15 | 527.67 | 16 |
| Warm day | 30 | 86 | 303.15 | 545.67 | 24 |
| Normal body temperature | 37 | 98.6 | 310.15 | 558.27 | 29.6 |
| Fever (adult) | 38 | 100.4 | 311.15 | 560.07 | 30.4 |
| Very hot day | 40 | 104 | 313.15 | 563.67 | 32 |
| C = F crossover | -40 | -40 | 233.15 | 419.67 | -32 |
| Water boils (sea level) | 100 | 212 | 373.15 | 671.67 | 80 |
Cooking temperatures
Temperature conversion matters most in cooking when working with recipes from another country. Below are the standard oven temperatures and safe internal meat temperatures used in professional cooking.
Oven temperatures
| Description | Celsius | Fahrenheit | Gas mark (UK) |
|---|---|---|---|
| Very slow / warm | 120°C | 250°F | ½ |
| Slow | 150°C | 302°F | 2 |
| Moderate | 180°C | 356°F | 4 |
| Moderately hot | 190°C | 374°F | 5 |
| Hot | 200°C | 392°F | 6 |
| Very hot | 220°C | 428°F | 7 |
| Extremely hot | 230°C | 446°F | 8 |
| Pizza / bread | 250°C | 482°F | 9 |
Note: fan-assisted (convection) ovens typically run 15-20°C (25-35°F) hotter than a conventional oven setting. If a recipe specifies a conventional oven, reduce the temperature by that amount for a fan oven.
Safe internal meat temperatures
The following are the minimum internal temperatures recommended by food safety authorities (US FDA / UK Food Standards Agency) for safely cooked meat.
| Meat | Celsius | Fahrenheit |
|---|---|---|
| Poultry (chicken, turkey) | 74°C | 165°F |
| Ground beef / pork | 71°C | 160°F |
| Whole beef, pork, lamb (medium) | 63°C | 145°F |
| Fish and shellfish | 63°C | 145°F |
| Leftovers and casseroles | 74°C | 165°F |
All conversion formulas
| From | To | Formula |
|---|---|---|
| °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 |
| °F | K | K = (°F - 32) × 5/9 + 273.15 |
| K | °F | °F = (K - 273.15) × 9/5 + 32 |
| °C | °R | °R = (°C + 273.15) × 9/5 |
| °F | °R | °R = °F + 459.67 |
| K | °R | °R = K × 9/5 |
| °C | °Ré | °Ré = °C × 4/5 |
| °Ré | °C | °C = °Ré × 5/4 |
Temperature differences vs absolute temperatures
This is the most misunderstood aspect of temperature conversion, and it causes real errors in cooking, engineering, and science.
When you convert a temperature value (a fixed point on a scale), you use the full formula including the offset: 20°C = 68°F.
But when you convert a temperature difference or change, you only use the scaling factor, not the offset.
$$\Delta F = \Delta C \times \frac{9}{5}$$
Examples:
- A rise of 5°C is a rise of 9°F (5 × 9/5 = 9). Not 41°F.
- If a recipe says "increase oven temperature by 10°C", that is an increase of 18°F.
- A fever of 1°C above normal (37°C) is a 1.8°F rise above normal, not a 33.8°F rise.
The confusion arises because 5°C (the temperature) converts to 41°F, while a 5°C change converts to a 9°F change. These look like different answers, but they are answering different questions.
Practical rule: if the question is "what temperature is X degrees?" use the full formula with the +32 offset. If the question is "how many degrees did it change by?" just multiply by 9/5 or 5/9 with no offset.
Common mistakes
Forgetting the offset in the Celsius-Fahrenheit formula
The most frequent error is multiplying Celsius by 1.8 (which is 9/5) without adding 32. This gives the right degree-size scaling but the wrong absolute temperature. Example: 100°C × 1.8 = 180, which is wrong. The correct answer is 180 + 32 = 212°F. Similarly, dividing Fahrenheit by 1.8 without first subtracting 32 gives an incorrect Celsius value.
Using the absolute formula for a temperature change
See the section above. If an oven recipe says 180°C and you need to add 20°C, the new temperature is 200°C = 392°F. Do not convert 20°C to 68°F and add that to 356°F. You are changing an absolute value, not adding an offset, so convert the final absolute temperature (200°C = 392°F).
Assuming water always boils at 100°C
Water boils at 100°C (212°F) at standard sea-level pressure (1 atm). At altitude, the boiling point drops. At Denver (1,609 m / 5,280 ft), water boils at about 94°C (201°F). At the top of Mount Everest (8,849 m), water boils at around 71°C (160°F) - barely hot enough to safely brew tea. This matters for any recipe or food safety calculation done at significant altitude.
Negative Celsius and negative Fahrenheit are different ranges
-5°C is cold but above the Fahrenheit zero: -5°C = 23°F. Fahrenheit zero (0°F = -17.8°C) is much colder. Many people assume negative Celsius and negative Fahrenheit overlap more than they do. The scales only cross at -40 degrees.
FAQs
How do I convert Celsius to Fahrenheit?
Multiply by 9/5 then add 32. Formula: °F = °C × 9/5 + 32. Example: 20°C × 9/5 = 36, + 32 = 68°F. Quick mental estimate: double the Celsius and add 30 (gives 70°F for 20°C, off by 2°F).
How do I convert Fahrenheit to Celsius?
Subtract 32 then multiply by 5/9. Formula: °C = (°F - 32) × 5/9. Example: 98.6°F - 32 = 66.6, × 5/9 = 37°C.
What temperature is the same in Celsius and Fahrenheit?
-40 degrees is the only temperature where both scales are equal. At any temperature above -40, Fahrenheit is always higher than Celsius. At any temperature below -40, Fahrenheit is always lower.
Can Kelvin be negative?
No. Kelvin starts at absolute zero (0 K = -273.15°C), the lowest possible temperature in the universe. There are no negative Kelvin values. Absolute zero has been approached to within a billionth of a degree in laboratory conditions but never fully reached.
What is absolute zero?
Absolute zero is 0 K, -273.15°C, or -459.67°F. It is the point at which all atomic thermal motion effectively ceases. It is theoretically unreachable because removing the last quanta of thermal energy from a system would require infinite work.
What is 180°C in Fahrenheit?
180°C = 356°F. Calculation: 180 × 9/5 + 32 = 324 + 32 = 356°F. This is a standard moderate oven temperature for baking cakes and roasting.
What is a normal body temperature in Fahrenheit?
Normal adult body temperature is 37°C = 98.6°F. A fever in adults is generally defined as 38°C (100.4°F) or above. Note that normal body temperature varies slightly by individual and time of day.
What is the difference between Kelvin and Celsius?
Kelvin and Celsius use identical degree sizes, so a change of 1 K is the same change as 1°C. The only difference is the zero point: 0 K = -273.15°C. To convert, add or subtract 273.15. Kelvin has no degree symbol because its zero is physically absolute, not arbitrary.
What is Rankine used for?
Rankine is used in US thermodynamics, aerospace engineering, and HVAC where absolute temperatures are needed but engineers work in Fahrenheit. It is the Fahrenheit counterpart of Kelvin: same degree size as Fahrenheit, but starting from absolute zero (0°R = 0 K = -273.15°C).