Temperature Converter

Temperature Conversion: Celsius, Fahrenheit, Kelvin and Rankine

Type a temperature, choose the units to convert from and to, and the converter shows the result straight away along with the formula it used, the value on all four scales and a thermometer marking where it sits against water freezing, room temperature, body temperature, a hot Australian summer day and water boiling. Whether you call it a temperature conversion calculator, a temp unit converter or a Celsius conversion, the arithmetic is the same.

Australia uses Celsius for weather, cooking and everyday life, but you will meet Fahrenheit in American recipes, appliances and websites, Kelvin in science and lighting (colour temperature), and Rankine in some engineering. There is also a Difference mode for converting a change in temperature, and an oven chart for gas marks and fan-forced settings.

Temperature Conversion Formulas

Worked Examples

25 °C to °F and K. 25 × 9/5 + 32 = 77 °F, and 25 + 273.15 = 298.15 K (536.67 °R).

98.6 °F to °C. (98.6 − 32) × 5/9 = 37 °C, which is 310.15 K: the usual figure quoted for normal body temperature, though individuals vary.

A 180 °C oven. 180 × 9/5 + 32 = 356 °F exactly. Recipes round this to 350 °F, which is gas mark 4. A fan-forced oven needs about 20 °C less, so 160 °C fan-forced is roughly equivalent. Going the other way, a recipe that says 180 °C for a fan-forced oven is about 200 °C conventional, which is 392 °F or gas mark 6.

A change of 10 °C. In Difference mode this is 18 °F, 10 K and 18 °R, with no offset added.

Temperature Readings and Temperature Differences

A reading says where you are on a scale, so each scale's zero matters. A difference says how far apart two readings are, so only the size of the degree matters. The Celsius and kelvin degrees are the same size, and the Fahrenheit and Rankine degrees are each 5/9 the size. That is why 10 °C is a reading of 50 °F, but a change of 10 °C is a change of 18 °F.

Oven Temperatures: Fan-Forced, Conventional and Gas Mark

Many recipes give a conventional oven temperature. A common rule for fan-forced ovens is to reduce it by about 20 °C, although ovens differ, so check the manual and watch the food. Gas marks run from 1 (140 °C, 275 °F) to 9 (240 °C, 475 °F) in the chart under the converter. The Fahrenheit and gas mark columns are the rounded values printed on dials and in recipes, which is why 180 °C shows as 350 °F rather than the exact 356 °F.

Frequently Asked Questions

What is the temperature conversion formula?

To convert Celsius to Fahrenheit, multiply by 9/5 and add 32: °F = °C × 9/5 + 32. To go back, subtract 32 and multiply by 5/9: °C = (°F − 32) × 5/9. For Kelvin, add 273.15 to Celsius (K = °C + 273.15). For example, 25 °C is 25 × 9/5 + 32 = 77 °F, and 98.6 °F is (98.6 − 32) × 5/9 = 37 °C.

How do I convert temperature from Celsius to Fahrenheit?

Multiply the Celsius value by 1.8 (that is 9/5) and add 32. So 0 °C is 32 °F, 25 °C is 77 °F, 37 °C is 98.6 °F and 100 °C is 212 °F. The converter above does it as you type and shows the formula for whichever pair of units you pick.

What is K conversion, and how do I convert Kelvin?

K means kelvin, the SI unit of temperature. Kelvin has no degree symbol and starts at absolute zero, so it is never negative: 0 K is −273.15 °C. To convert, use °C = K − 273.15 and K = °C + 273.15. For example, 0 °C is 273.15 K, and 300 K is 26.85 °C (80.33 °F).

What are the temperature conversions formulas for all four scales?

Via Celsius: °F = °C × 9/5 + 32, K = °C + 273.15 and °R = (°C + 273.15) × 9/5. Rankine uses Fahrenheit-sized degrees starting at absolute zero, so °R = °F + 459.67, and K = °R × 5/9. At 25 °C that gives 77 °F, 298.15 K and 536.67 °R.

Is there a temperature conversion calculator for oven temperatures and gas marks?

Yes. Open the oven chart under the converter. A 180 °C conventional oven is 356 °F exactly, and recipes round that to 350 °F, which is gas mark 4. For a fan-forced oven, a common rule is to reduce the conventional temperature by about 20 °C, so 160 °C fan-forced is roughly the same as 180 °C conventional. Treat fan-forced figures as approximate.

Which temperature is the same in Celsius and Fahrenheit?

−40. At −40 °C the Fahrenheit reading is also −40 °F, because −40 × 9/5 + 32 = −40. It is the only point where the two scales agree, and it is in the common conversions table with the Kelvin value (233.15 K).

What is a temperature difference (interval) conversion?

When you convert a change in temperature rather than a reading, you leave out the +32 and +273.15 offsets and only scale. A rise of 10 °C is a rise of 18 °F and of 10 K. Use the Difference mode for questions like how much hotter one day was than another. Using the absolute formula on a difference gives the wrong answer (10 °C is a reading of 50 °F, not a change of 50 °F).

What temperature is too low to convert?

Nothing can be colder than absolute zero: 0 K, −273.15 °C or −459.67 °F. The converter shows an error for readings below it. Differences have no such limit, because a change of −500 °C is just a size of change, not a position on the scale.

Is this temp unit converter accurate?

The conversions use the exact definitions: K = °C + 273.15, and the Fahrenheit degree is exactly 5/9 of a kelvin. Results are shown to up to 10 significant digits, and you can choose a fixed number of decimal places. Oven gas marks are a different matter: they are rounded dial values, not exact conversions.