°C to K: formula K = °C × 1 + 273.15

The formula

K = °C × 1 + 273.15

Where the factor comes from — each unit by its definition, then its size in SI:

T(K) = (T(°C) + 273.15) × 1
1 K is the SI unit of temperature.

Gas laws and radiation formulas need absolute temperature in kelvin. Celsius and kelvin differ by an offset only; Fahrenheit differs in both offset and step size, so it is a formula, not a single factor.

Worked examples

Water freezing: 0 °C = 273.15 K — 0 × 1 + 273.15 = 273.15
Human body temperature: 37 °C = 310.15 K — 37 × 1 + 273.15 = 310.15
A baking oven (350 °F): 176.667 °C = 449.817 K — 176.667 × 1 + 273.15 = 449.817
A warm room: 20 °C = 293.15 K — 20 × 1 + 273.15 = 293.15

Frequently asked questions

How many kelvin is 1 °C?

1 °C = 274.15 K. The rule is K = °C × 1 + 273.15.

How do I convert kelvin back to degrees Celsius?

Invert the rule: °C = (K − 273.15) / 1.

°C to K conversion table

Degrees Celsius (°C)	Kelvin (K)
-40	233.15
-30	243.15
-20	253.15
-10	263.15
-5	268.15
0	273.15
5	278.15
10	283.15
15	288.15
20	293.15
25	298.15
30	303.15
35	308.15
37	310.15
40	313.15
50	323.15
60	333.15
70	343.15
80	353.15
90	363.15
100	373.15
150	423.15
200	473.15
250	523.15
300	573.15

Definitions: BIPM, The International System of Units (SI Brochure), 9th edition (2019), Tables 2, 4 and 8 — https://www.bipm.org/en/publications/si-brochure. Machine value of the factor: 1, offset 273.15.