Temperature Converter – Celsius, Fahrenheit and Kelvin

Temperature formulas

Temperature scales do not share a common zero, so they cannot be converted with a single factor. The converter uses these formulas:

• Celsius to Fahrenheit: °F = °C × 9/5 + 32
• Fahrenheit to Celsius: °C = (°F − 32) × 5/9
• Celsius to Kelvin: K = °C + 273.15
• Kelvin to Celsius: °C = K − 273.15

For example, 25 °C × 1.8 = 45, plus 32 gives 77 °F. Going back, 77 − 32 = 45, and 45 × 5/9 = 25 °C.

Reference points

Water freezes at 0 °C (32 °F, 273.15 K) and boils at 100 °C (212 °F) at sea level. Normal body temperature is about 37 °C (98.6 °F), and a fever usually starts around 38 °C (100.4 °F). At −40 the Celsius and Fahrenheit scales meet: −40 °C is exactly −40 °F. Absolute zero, the lowest possible temperature, is 0 K or −273.15 °C.

Oven temperatures

Recipes from the United States list oven temperatures in Fahrenheit. Common settings are 350 °F (177 °C, usually rounded to 180 °C), 375 °F (190 °C), 400 °F (204 °C, often 200 °C) and 425 °F (218 °C, often 220 °C). For a fan oven, many recipes suggest lowering the temperature by about 20 °C.

Quick estimate

To approximate Fahrenheit from Celsius, double the Celsius value and add 30: 20 °C gives about 70 °F (exactly 68 °F). The estimate is good for weather, but use the exact formula for cooking, medicine or science.

Temperature differences

A change of 1 °C equals a change of 1.8 °F and of 1 K. When converting a difference rather than a reading, such as “the room warmed by 5 °C”, multiply by 1.8 without adding 32: the room warmed by 9 °F.

Sources

Conversion factors follow the SI definitions in the BIPM SI Brochure and the exact factors for US customary and imperial units in NIST Special Publication 811.