About the Temperature Converter
Temperature is the one everyday measurement that cannot be converted with a single multiplication. Celsius, Fahrenheit, kelvin and Rankine not only use degrees of different sizes, they also start from different zero points. That is why 0 °C is 32 °F, not 0 °F, and why a 10-degree rise in Celsius is an 18-degree rise in Fahrenheit rather than a 50-degree one. Weather forecasts, oven settings, fever thermometers, lab work and engineering specifications all need the right formula for the job.
This temperature converter converts between Celsius, Fahrenheit, kelvin and Rankine. It handles two different kinds of conversion: a reading — a temperature shown on a thermometer — and a difference — how much a temperature rose, fell or varies. It shows the formula, the value on every scale, and what the temperature means in everyday terms.
How to Use the Temperature Converter
Choose whether you are converting a reading or a difference or change.
Enter the value. Readings can be negative, down to absolute zero.
Choose the scale to convert from and to.
The result appears with the formula used and the temperature on all four scales.
The Conversion Formulas
Celsius → Fahrenheit °F = °C × 9/5 + 32
Fahrenheit → Celsius °C = (°F − 32) × 5/9
Celsius → kelvin K = °C + 273.15
Fahrenheit → Rankine °R = °F + 459.67
differences: 1 °C change = 1 K change = 1.8 °F change = 1.8 °R changeThe factor 9/5, or 1.8, comes from the size of the degrees: there are 100 Celsius degrees between the freezing and boiling points of water, but 180 Fahrenheit degrees. The 32 comes from where each scale puts freezing: 0 °C but 32 °F.
Step-by-Step Example
25 °C to Fahrenheit.
25 × 9/5 = 45
45 + 32 = 77 °FSo 25 °C is 77 °F, a warm day. On the other scales it is 298.15 K and 536.67 °R.
98.6 °F to Celsius.
98.6 − 32 = 66.6
66.6 × 5/9 = 37 °CThe classic normal body temperature is exactly 37 °C.
A change of 10 °C is 10 × 1.8 = 18 °F, with no 32 added, because a change has no zero point to shift.
Readings and Differences
This distinction catches out many people. If the forecast says tomorrow will be 10 °C warmer, that is 18 °F warmer — not 50 °F, which is what the reading formula would give. The same applies to temperature ranges, tolerances and changes in science and engineering: a process that must stay within ±2 °C must stay within ±3.6 °F. Choose difference or change in the converter for any figure that describes how much, not how hot.
Reference Temperatures
absolute zero −273.15 °C −459.67 °F 0 K
−40 (both scales) −40 °C −40 °F 233.15 K
water freezes 0 °C 32 °F 273.15 K
room temperature 20–22 °C 68–72 °F
body temperature 37 °C 98.6 °F 310.15 K
water boils (sea level) 100 °C 212 °F 373.15 K
moderate oven 180 °C 356 °FA useful quick estimate from Celsius to Fahrenheit is to double and add 30: 20 °C becomes 70 °F against the exact 68. It works best between about 0 and 30 °C.
The Four Scales
Celsius sets 0 at the freezing point of water and 100 at its boiling point at sea level. It is used for weather and everyday life in almost every country.
Fahrenheit is used for weather and cooking in the United States and a few other places. Its 0 and 96 were originally set by a brine mixture and human body temperature.
Kelvin is the SI unit, used throughout science. It starts at absolute zero and uses degrees the same size as Celsius. It is written without a degree sign: 300 K.
Rankine starts at absolute zero with Fahrenheit-sized degrees. It is used mainly in some US engineering fields, such as thermodynamics and aerospace.
Absolute Zero
No temperature can go below absolute zero, −273.15 °C, where the particles in matter have the least energy they can possibly have. Scientists have cooled atoms to within a billionth of a degree of it, but never reached it. The converter rejects readings below absolute zero, since they cannot exist. Differences, though, can be any size or sign.
Oven Temperatures
Oven settings are where a wrong conversion is most noticeable. British and European recipes give Celsius, and sometimes a gas mark; American recipes give Fahrenheit. Common pairs, rounded the way recipes usually round them, are 150 °C for 300 °F, 160 °C for 325 °F, 180 °C for 350 °F, 200 °C for 400 °F and 220 °C for 425 °F. Fan ovens cook faster, so recipes written for conventional ovens are often reduced by about 20 °C for a fan oven. The exact conversion of 180 °C is 356 °F, but a 350 °F setting works just as well because ovens themselves are rarely accurate to within 5 degrees.
Understanding Your Result
The headline is the converted temperature, or the converted change.
The formula line shows the formula used for that pair of scales.
The on every scale line gives the value in all four units.
The what it means line describes the temperature in everyday terms, or reminds you that a difference is a change, not a reading.
When Should You Use This Calculator?
Use it for weather forecasts and travel in countries that use the other scale.
Use it for oven temperatures and recipes from abroad.
Use it for fever and body temperature readings.
Use it for science, where kelvin is required, and for engineering tolerances and temperature changes.
Common Mistakes
Converting a change with the reading formula. A 10 °C rise is 18 °F, not 50 °F.
Forgetting the order of operations. For Fahrenheit to Celsius, subtract 32 before multiplying by 5/9.
Writing "degrees kelvin". Kelvin has no degree sign: it is 300 K, not 300 °K.
Using the double-and-add-30 shortcut for cooking. At oven temperatures it is far out; use the exact formula.
Entering temperatures below absolute zero. −300 °C is impossible.