Temperature Converter

How this temperature conversion is calculated

The page converts through Celsius, then out to the unit you picked. Fahrenheit to Celsius is (F − 32) × 5 ÷ 9. Celsius to Fahrenheit is C × 9 ÷ 5 + 32. Kelvin to Celsius is K − 273.15. Celsius to kelvin is C + 273.15. A Fahrenheit-to-kelvin conversion does the Fahrenheit step first and then adds 273.15. The result line rounds to four decimal places. The line that shows all three scales rounds each of them to two decimal places. Those are different roundings of the same Celsius value, so the result and the three-scale line can disagree in the last digits.

If the Celsius value is strictly below −273.15, the page stops, warns you, and hides the result. −273.15°C is allowed. It is 0 K and −459.67°F. There is no gas mark, no Rankine scale, and no wind-chill or heat-index adjustment. Oven gas marks are a lookup table on the Oven Temperature Converter, and that page rounds whole degrees differently from this one.

Worked examples

Example 1: Freezing, boiling, and the −40 check

32°F converts to 0°C and the three-scale line shows 32°F = 0°C = 273.15 K. 212°F converts to 100°C, and the three-scale line shows 212°F = 100°C = 373.15 K. 0°C to Fahrenheit is 32. 100°C to kelvin is 373.15. Enter −40°F. (−40 − 32) × 5 ÷ 9 = −40, so Celsius is −40 as well. The three-scale line shows −40°F = −40°C = 233.15 K. That coincidence is a useful check that the offset and the 5/9 factor are both in the path. A converter that only shifts by 32 will not land on −40.

Example 2: 98.6°F, 20°C, and 72°F

98.6°F: (98.6 − 32) × 5 ÷ 9 = 37 exactly. The result is 37°C. The three-scale line shows 98.6°F = 37°C = 310.15 K. This page converts 98.6. It does not decide whether 98.6 is a useful clinical reference. 20°C to Fahrenheit is 20 × 9 ÷ 5 + 32 = 68 exactly, and kelvin is 293.15. 72°F to Celsius is (72 − 32) × 5 ÷ 9 = 22.222…, so the result displays as 22.2222°C and the three-scale line shows 22.22°C and 295.37 K.

Example 3: Absolute zero, and 350°F beside the oven page

0 K converts to −273.15°C and −459.67°F. The three-scale line shows −459.67°F = −273.15°C = 0 K. A Celsius input of −273.16 is below the cutoff, so the page warns and shows no result. 350°F on this page displays as 176.6667°C, and the three-scale line shows 350°F = 176.67°C = 449.82 K. The oven tool's summary line for the same 350°F says 177°C and also names gas mark 4. Both pages use (350 − 32) × 5 ÷ 9. They round the display differently, and only the oven page has the gas-mark table. Use this page when you need kelvin or a four-decimal Celsius. Use the oven page when the dial says Gas Mark.

When to use this

Use it for a weather report, a thermostat, a lab bath, a fever number someone wrote in the other scale, or any Fahrenheit, Celsius, or kelvin value that is not a gas mark. Baking setpoints that have to become a gas mark belong on the oven converter. A length, a weight, or a volume that happens to sit next to a temperature in a spec is still a different quantity. Those converters do not call this one.

A difference of 10 degrees Celsius is the same size as a difference of 10 kelvin, because the scales share a degree size and differ only by 273.15. A reading of 20°C is not "twice" a reading of 10°C. On the kelvin line those temperatures are 293.15 K and 283.15 K. The page will convert either number. It will not form the ratio for you. If a formula in a textbook asks for absolute temperature, convert to kelvin first and then leave this page.

What the cutoff is, and what elevation is not

The absolute-zero check uses the Celsius value after conversion, and it uses a strict less-than. 0 K and −273.15°C convert. One hundredth of a degree below that does not. The check is there to catch a sign error, not to model a physical apparatus. Boiling at 100°C and freezing at 0°C on this page are the definitions of the scale points at standard conditions. The page does not lower the boiling point for elevation. If you are at altitude, the thermometer reading still converts by the formula. The temperature at which your water boils is a measurement, not a conversion.

Common mistakes

• Dropping the 32. Multiplying Fahrenheit by 5 ÷ 9 without subtracting 32 first will not match the panel. 32°F is 0°C, not 17.8°C.
• Using this page for gas mark. There is no gas-mark menu. 350°F here is 176.6667°C. The oven page is where gas mark 4 is defined as 180°C in its table.
• Reading 98.6°F to 37°C as a medical claim. The arithmetic is exact: (98.6 − 32) × 5 ÷ 9 = 37. What that means for a person is not computed.
• Calling 20°C twice 10°C. The Celsius numbers double. The kelvin numbers are 293.15 and 283.15. This page shows both so the absolute scale is visible.
• Expecting the four-decimal result and the two-decimal summary to match digit for digit. 72°F displays as 22.2222°C on the result and 22.22°C on the three-scale line.
• Feeding a below-zero kelvin guess. Negative kelvin is below the cutoff once it becomes Celsius under −273.15, and the result stays hidden.

Limitations

Three scales, one direction per press, four decimal places on the result, two on the combined line. No gas mark, no Rankine, no altitude, no wind chill, no heat index, and no medical interpretation. The 273.15 offset is exact in the formula. Display rounding is not. Half-steps round by the same half-up rule as the other calculators on the site. A thermometer that reads in whole degrees has already rounded before you type.

77°F converts to 25°C exactly, because (77 − 32) × 5 ÷ 9 = 25, and 25°C converts back to 77°F. The three-scale line shows 77°F = 25°C = 298.15 K. It is a cleaner check than 72°F, which is not a whole Celsius degree: that one displays as 22.2222°C on the result and 22.22°C on the summary, with 295.37 K beside it.

FAQ

Why is 32°F exactly 0°C and 273.15 K?

Because (32 − 32) × 5 ÷ 9 = 0, and kelvin is that Celsius value plus 273.15. 212°F is 100°C and 373.15 K by the same path.

What does −40 convert to?

−40°F converts to −40°C. The three-scale line shows −40°F = −40°C = 233.15 K. It is the point where the Fahrenheit and Celsius formulas meet.

How does this page treat absolute zero?

0 K displays as −273.15°C and −459.67°F. An input that converts to a Celsius value below −273.15 is rejected and the result is hidden. −273.15°C itself is allowed.

Why is 350°F 176.6667°C here and 177°C on the oven page?

Both start from (350 − 32) × 5 ÷ 9. This page shows four decimal places on the result, 176.6667, and two on the summary, 176.67. The oven page rounds its summary to a whole degree, 177, and also maps the value to gas mark 4.

Is 98.6°F a special body temperature on this page?

Only arithmetically. It converts to 37°C and 310.15 K exactly. The page does not compare it with a normal range or give advice about a fever.

Do I use kelvin for weather?

The page will convert a weather temperature into kelvin if you ask. Daily forecasts are not written that way. Kelvin is the scale to use when a formula needs an absolute temperature. 20°C is 293.15 K, not "twice" 10°C.

Can this convert a gas mark?

No. Gas marks are a table on the Oven Temperature Converter, not a linear unit. Convert Fahrenheit or Celsius here, and use the oven page when the recipe names a gas mark.

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