What formula converts Celsius to Fahrenheit?

Multiply by 9/5 and add 32: F = C × 9/5 + 32. To go back, subtract 32 then multiply by 5/9. The two scales meet at minus 40 degrees, where C and F are equal.

How does Kelvin relate to Celsius?

Kelvin uses the same degree size as Celsius but starts at absolute zero, so K = C + 273.15. 0 Kelvin is the coldest possible temperature, equal to minus 273.15 Celsius.

What is the Rankine scale?

Rankine is to Fahrenheit what Kelvin is to Celsius: an absolute scale with Fahrenheit-sized degrees. R = F + 459.67, and R = K × 9/5. It is used in some US engineering thermodynamics.

Why is the conversion not a single factor?

Celsius and Fahrenheit have different zero points, so converting needs both a scale (9/5) and an offset (+32). Only the absolute scales (Kelvin, Rankine) relate to each other by a pure factor of 9/5.

Does this tool work offline?

Yes. Every conversion runs locally in your browser with JavaScript. No data is uploaded, logged or stored.

Temperature Unit Conversion Reference

Email me this result

Get this tool's output sent to your inbox, plus one useful tool a week. No spam, unsubscribe any time.

Convert between all four temperature scales

Temperature is the one common conversion where you cannot just multiply by a factor, because the scales start at different zero points. This reference converts between Celsius, Fahrenheit, Kelvin and Rankine using the exact formulas, and shows where your value sits against fixed physical reference points.

How it works

Each input is converted to Celsius as a pivot, then out to every scale:

C -> F :  F = C × 9/5 + 32
C -> K :  K = C + 273.15
C -> R :  R = (C + 273.15) × 9/5

To convert into Celsius first, the formulas are reversed: subtract the offset before applying the scale factor. Celsius and Fahrenheit need both a factor (9/5) and an offset (+32); Kelvin and Rankine are absolute scales that share zero with absolute zero (-273.15 C).

Tips and notes

Celsius and Fahrenheit read the same value at exactly -40 degrees.
Absolute zero is 0 K, -273.15 C, -459.67 F, 0 R — nothing can be colder.
Water freezes at 0 C / 32 F and boils at 100 C / 212 F at standard pressure.
A change of 1 K equals a change of 1 C, and a change of 1 R equals a change of 1 F.