Temperature Converter

How temperature conversion works

Temperature scales differ in both step size and zero point, so converting between them uses formulas rather than simple factors. The converter routes every conversion through Celsius and supports Fahrenheit, Kelvin, and Rankine.

Formulas

°F = °C × 9/5 + 32

°C = (°F − 32) × 5/9

K = °C + 273.15

°R = (°C + 273.15) × 9/5

Reference points

Worked example

Converting 20 °C to Fahrenheit: 20 × 9/5 + 32 = 36 + 32 = 68 °F — a mild spring day. The same 20 °C is 293.15 K.

Which scale is used where

Celsius is the everyday scale in most of the world and in science; Fahrenheit stays in common use in the United States for weather, cooking, and body temperature; Kelvin is the SI unit for scientific work because it starts at absolute zero and has no negative values; and Rankine is Kelvin's Fahrenheit-sized counterpart, still seen in some US engineering fields.

Handy landmarks to memorize

A few anchor points make quick estimates easy without a formula. −40° is the one temperature where Celsius and Fahrenheit meet. 16°C ≈ 61°F is a cool room, 28°C ≈ 82°F is a hot day, and 180°C ≈ 350°F is a common baking temperature. For a rough mental conversion from Celsius to Fahrenheit, double the number and add 30 — close enough for weather, though the calculator gives the exact value.

Celsius, Fahrenheit, and Kelvin formulas

Order matters in both directions. Going to Fahrenheit you scale first and add 32 last; coming back you subtract 32 first and scale after. Reversing either sequence is the single most common mistake in the conversion.

Kelvin has no degree sign and no negative values — 0 K is absolute zero, so the offset is a straight addition with no scaling, because a kelvin and a degree Celsius are the same size.

Celsius and centigrade are the same scale

"Centigrade" was the original name, from the hundred gradations between the freezing and boiling points of water. It was renamed Celsius in 1948 to honour Anders Celsius and to avoid a clash with the grad, a unit of angle also called the centigrade. Nothing about the scale changed, so converting centigrade to Celsius is a conversion between a unit and its own former name — the number is identical.

Conversion chart

For a quick mental estimate, double the Celsius figure and add 30. At 20 °C that gives 70 °F against a true 68 — near enough for weather, and increasingly wrong at oven temperatures.

Temperature does not convert to pressure, energy, or humidity

Degrees measure how hot something is, not how much energy it holds or how hard it pushes — so these need more than a temperature:

• Celsius to joules — needs mass and specific heat capacity: energy = mass × specific heat × temperature change. Heating 1 kg of water by 1 °C takes 4,186 J; the same rise in 1 kg of iron takes 449 J.
• Celsius to bar or atm — a gas law relationship, not a conversion. Pressure changes with temperature only when volume and quantity are held fixed, and Kelvin must be used rather than Celsius.
• Celsius to humidity — relative humidity is the ratio of actual water vapour to the maximum the air could hold at that temperature. Temperature sets the ceiling, so the same air becomes "drier" in relative terms as you warm it, without losing any water at all.

For lengths, weights, areas, and volumes, use the unit converter.