Temperature Converter: Fahrenheit, Celsius, Kelvin and Rankine

The Fahrenheit and Celsius formulas, with a worked example

Fahrenheit and Celsius use different zero points and different step sizes. Water freezes at 32 degrees Fahrenheit and 0 degrees Celsius, and boils at 212 and 100. That means 180 Fahrenheit degrees span the same range as 100 Celsius degrees, a ratio of 9 to 5. To convert Fahrenheit to Celsius, subtract 32 and multiply by 5/9. To go the other way, multiply by 9/5 and add 32.

Worked example: a body temperature of 98.6 degrees Fahrenheit. Subtract 32 to get 66.6, then multiply by 5/9 to get 37.0 degrees Celsius. Check it in reverse: 37 times 9/5 is 66.6, plus 32 is 98.6. The page runs the same steps through Kelvin, so a temperature in any of the four scales lands in the other three without rounding errors building up along the way. Use it for cooking, weather forecasts, aquarium heaters, camping stoves and science homework. Results show one decimal in the big number and two in the rows.

Kelvin is the scientific scale. Its zero is absolute zero, and one Kelvin step equals one Celsius step, so K = C + 273.15. Rankine does the same for Fahrenheit: R = F + 459.67. A quick mental estimate for weather is to double the Celsius value and add 30, which gets within a few degrees in normal weather. For cooking, use the exact formula. If you are checking a packing list or weather forecast abroad, see the miles to km converter for the distance side of the trip.

Reference table of key temperatures. It is plain HTML, so it stays visible without JavaScript.

Where these numbers come from

The formulas and default values in this calculator are based on:

• NIST unit conversion guidance (nist.gov/pml/owm/metric-si/unit-conversion)
• NIST SP 811 Appendix B temperature entries. Note: reference-table values for the oven and body temperature are rounded

This is a planning estimate, not medical, legal or immigration advice. Fees, allowances, limits and entry rules change, so confirm the figures with your airline, cruise line, customs agency or the official government source before you book or travel, and follow their rules if they differ from this page.