acalculator

Temperature conversion calculator

Enter a temperature, pick the scale it is on and the scale you want. The answer, the formula, and the same temperature on all four scales update as you type.

Your numbers

Converted temperature
20

68 Fahrenheit (°F) = 20 Celsius (°C).

Celsius (°C)
20
Fahrenheit (°F)
68
Kelvins (K)
293.15
Rankine (°R)
527.67
Formula
°C = (°F − 32) × 5 ÷ 9

Converted temperature: 20. 68 Fahrenheit (°F) = 20 Celsius (°C).

How to calculate

Converts a temperature between Celsius, Fahrenheit, kelvins, and Rankine, with the formula for each pair.

Example with the default inputs (Temperature 68, From Fahrenheit (°F), To Celsius (°C)): 68 Fahrenheit (°F) = 20 Celsius (°C).

Method: kelvins = (t + offset) × scale for the "From" scale, then back out on the "To" scale

  • °C = K − 273.15 and °F = K × 9 ÷ 5 − 459.67 (NIST SP 811). Rankine is kelvins × 9 ÷ 5: Fahrenheit-sized degrees from absolute zero.
  • The arithmetic is exact on the decimal you type; each answer is rounded once, and the page shows at most 6 decimal places.
  • A temperature below absolute zero (0 K) has no answer.

Machine-readable copies: Markdown, JSON.

Worked examples

Each example is checked against the calculator on every build.

  1. Temperature 68, From Fahrenheit (°F), To Celsius (°C) gives Converted temperature 20, Kelvins (K) 293.15, Rankine (°R) 527.67, Formula °C = (°F − 32) × 5 ÷ 9.Source: NIST SP 811 (2008), section 4.2.1.1 and Appendix B.8: (68 − 32) × 5 ÷ 9 = 20 °C
  2. Temperature 100, From Celsius (°C), To Fahrenheit (°F) gives Converted temperature 212, Kelvins (K) 373.15, Rankine (°R) 671.67.Source: NIST SP 811 (2008), section 4.2.1.1: 100 × 9 ÷ 5 + 32 = 212 °F
  3. Temperature 98.6, From Fahrenheit (°F), To Celsius (°C) gives Converted temperature 37, Celsius (°C) 37, Kelvins (K) 310.15.Source: NIST SP 811 (2008), Appendix B.8: (98.6 − 32) × 5 ÷ 9 = 37 exactly
  4. Temperature -40, From Celsius (°C), To Fahrenheit (°F) gives Converted temperature -40, Kelvins (K) 233.15.Source: NIST SP 811 (2008), section 4.2.1.1: −40 × 9 ÷ 5 + 32 = −40
  5. Temperature 0, From kelvins (K), To Fahrenheit (°F) gives Converted temperature -459.67, Celsius (°C) -273.15, Rankine (°R) 0.Source: NIST SP 811 (2008), Appendix B.8: 0 K = −273.15 °C = −459.67 °F
  6. Temperature 500, From Rankine (°R), To kelvins (K) gives Converted temperature 277.777778, Fahrenheit (°F) 40.33.Source: NIST SP 811 (2008), Appendix B.8: K = °R × 5 ÷ 9 = 2,500 ÷ 9

How it works

Every scale has a fixed link to kelvins, the SI unit of temperature (NIST SP 811):

ScaleKelvins from a temperature t
Celsius (°C)K = t + 273.15
Fahrenheit (°F)K = (t + 459.67) × 5 ÷ 9
kelvins (K)K = t
Rankine (°R)K = t × 5 ÷ 9

The converter turns your temperature into kelvins, then turns the kelvins into the scale you want with the same line read backwards. For each pair it shows the direct formula:

  • °F = °C × 9 ÷ 5 + 32, and °C = (°F − 32) × 5 ÷ 9
  • K = °C + 273.15, and °C = K − 273.15
  • K = (°F + 459.67) × 5 ÷ 9, and °F = K × 9 ÷ 5 − 459.67
  • °R = (°C + 273.15) × 9 ÷ 5, and °C = °R × 5 ÷ 9 − 273.15
  • °R = °F + 459.67, and °F = °R − 459.67
  • °R = K × 9 ÷ 5, and K = °R × 5 ÷ 9

The result panel also shows the temperature on all four scales.

Rules

  • The temperature may be negative, from −1,000,000,000 to 1,000,000,000 on the "From" scale.
  • A temperature below absolute zero (below 0 K) has no answer: the page shows a message instead.
  • The arithmetic is exact. The calculator reads the decimal you type as an exact fraction, uses the exact offsets 273.15 and 459.67 and the exact factor 5/9, and rounds only the final answer to the nearest double-precision number. So 98.6 °F gives exactly 37 °C.
  • The page shows at most 6 decimal places, rounded half up from the decimal value. This holds for up to 14 significant digits. A longer shown number (100,000,000 or more with 6 decimals) is rounded from the double-precision answer, so its last digit can be 1 off.

Worked examples by hand

68 °F to °C. (68 − 32) × 5 ÷ 9 = 36 × 5 ÷ 9 = 20 °C. In kelvins: 20 + 273.15 = 293.15 K. In Rankine: 68 + 459.67 = 527.67 °R.

100 °C to °F. 100 × 9 ÷ 5 + 32 = 180 + 32 = 212 °F; 373.15 K; 671.67 °R.

98.6 °F to °C. (98.6 − 32) × 5 ÷ 9 = 66.6 × 5 ÷ 9 = 333 ÷ 9 = 37 °C, or 310.15 K.

−40 °C to °F. −40 × 9 ÷ 5 + 32 = −72 + 32 = −40 °F; 233.15 K.

0 K to °F. 0 × 9 ÷ 5 − 459.67 = −459.67 °F, which is −273.15 °C and 0 °R.

500 °R to K. 500 × 5 ÷ 9 = 277.777… K. In Fahrenheit: 500 − 459.67 = 40.33 °F.

Other questions people ask

How do I convert Fahrenheit to Celsius?

Subtract 32, then multiply by 5 and divide by 9. For example, 68 °F is (68 − 32) × 5 ÷ 9 = 20 °C.

How do I convert Celsius to Fahrenheit?

Multiply by 9, divide by 5, then add 32. For example, 100 °C is 100 × 9 ÷ 5 + 32 = 212 °F, the boiling point of water at sea level.

How do I convert Celsius to kelvins?

Add 273.15. A kelvin is the same size as a degree Celsius, and 0 K is absolute zero, −273.15 °C. So 20 °C is 293.15 K.

At what temperature are Celsius and Fahrenheit the same?

At −40. Put −40 into °F = °C × 9 ÷ 5 + 32 and you get −72 + 32 = −40.

What is the Rankine scale?

Rankine counts Fahrenheit-sized degrees from absolute zero, the way kelvins count Celsius-sized degrees. °R = °F + 459.67, and °R = K × 9 ÷ 5. Some US engineering tables use it.

Why can I not enter a temperature below absolute zero?

Absolute zero (0 K, −273.15 °C, −459.67 °F, 0 °R) is the lowest temperature there is. A colder value has no answer, so the page says so instead of converting it.

Is normal body temperature 37 °C exactly 98.6 °F?

Yes, as a conversion. 37 × 9 ÷ 5 + 32 = 98.6 exactly. The converter keeps the arithmetic exact, so 98.6 °F gives 37 °C, not 36.99999.