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Temperature Converter

Weather apps pick their scale by country: 25 °C in Delhi reads 77 °F in New York, and a freezer at −18 °C is 0 °F. Recipes, medical leaflets and physics pages add kelvin, where zero sits at the coldest temperature nature allows. This converter works in all three directions and shows the formula it used, so you can check any thermometer reading by hand.

Enter values

Absolute zero is −273.15 °C, so nothing goes below it

Celsius for weather and cooking, Fahrenheit for US recipes

Results update as you type.

Results

In Fahrenheit (°F)
77
In Celsius (°C)
25
In Kelvin (K)
298.15
Formula
°F = °C × 9/5 + 32

How is the Temperature Converter calculated?

Enter a temperature and choose the scale it is written in. You immediately get the reading in the other two scales — 25 °C becomes 77 °F and 298.15 K — plus the formula for the pair you picked, such as °F = °C × 9/5 + 32. Nothing goes below absolute zero: the form stops at −273.15 °C, which is 0 K, and rejects anything colder.

Formula

°F = °C × 9/5 + 32 · °C = (°F − 32) × 5/9 · K = °C + 273.15 · °C = K − 273.15. Celsius and Fahrenheit share a step size ratio of 9:5 but anchor their zeros differently; kelvin copies the Celsius step and drops the offset entirely. The fixed points: water freezes at 0 °C = 32 °F = 273.15 K.

Example

A cold snap of −18 °C is (−18 × 9/5) + 32 = −0.4 °F, essentially zero Fahrenheit — which is why the scales feel interchangeable near freezing. Body temperature of 98.6 °F is (98.6 − 32) × 5/9 = 37 °C exactly. And the famous crossover: at −40 the two scales meet, so −40 °C = −40 °F with no rounding anywhere.

Things to remember

For a quick estimate, subtract 30 and halve to go Fahrenheit to Celsius, or double and add 30 to go Celsius to Fahrenheit — a sanity check only, since the error grows away from room temperature. When precision matters, use the exact formulas above: they are definitions, valid from absolute zero to a blast furnace.

Frequently Asked Questions

How do I convert Celsius to Fahrenheit quickly?

Multiply by 9/5 (or 1.8) and add 32. So 20 °C × 1.8 = 36, plus 32 gives 68 °F. For mental arithmetic, double the Celsius and add 30: 25 °C comes out near 80 °F instead of the exact 77 °F.

What is minus 40 degrees Celsius in Fahrenheit?

−40 °F. It is the single point where the two scales coincide: (−40 × 9/5) + 32 = −72 + 32 = −40. The equality is exact rather than a rounding accident, which is why it turns up as an exam question so often.

Why does 0 K equal minus 273.15 °C?

Kelvin starts at absolute zero, where particles have the least motion quantum mechanics allows, and that point is defined as −273.15 °C (−459.67 °F). Converting is therefore pure addition: add 273.15 to Celsius for kelvin, subtract it to come back.

Which temperature conversions should I memorise?

Water's three anchors: freezing 0 °C = 32 °F, body temperature 37 °C = 98.6 °F, and boiling 100 °C = 212 °F. Anything between them you can interpolate, and the calculator handles everything else — including kelvin — without needing a mnemonic.

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