Temperature Converter Online Free

How to Convert Temperature

1. 1Select the source scale from the From dropdown — e.g. Celsius.
2. 2Enter a temperature value. The result updates instantly and the formula is shown below the converter.
3. 3See all scales at once in the all conversions table — useful for quick cross-reference.

Why Temperature Conversion Needs a Formula

Unlike units of length or weight, temperature scales differ in two ways: the size of a degree and the location of zero. Celsius and Fahrenheit both use different degree intervals (a 1 °C change equals a 1.8 °F change) and different zero points (0 °C = 32 °F). Converting between them requires both a multiplication and an addition. Kelvin and Rankine are absolute scales that start at absolute zero, making conversions to and from them simpler (just add or subtract 273.15 or 459.67 respectively).

Worked Example: Converting a UK Recipe Oven Temperature

A British recipe calls for baking at 180 °C (also labelled "Gas Mark 4"). An American oven dial is calibrated in Fahrenheit, so the conversion is (180 × 9/5) + 32 = 324 + 32 = 356 °F. Since most US oven dials move in 25° increments, a baker would round down to the nearest marked setting — 350 °F — which is close enough that recipe timing needs no adjustment.

This 6 °F gap between the exact conversion (356 °F) and the practical dial setting (350 °F) is a good illustration of why the reference table above shows precise values: for baking, rounding to the nearest dial marking is fine, but for lab work or industrial processes where a few degrees change an outcome, using the exact converted figure instead of a rounded rule of thumb matters.

Where Each Scale Comes From

The three everyday scales were each designed around different reference points, which is exactly why converting between them needs a formula rather than a single multiplier. Fahrenheit, devised by Daniel Gabriel Fahrenheit in 1724, originally anchored zero to a freezing brine mixture and set body temperature near 96; on the modern scale water freezes at 32 °F and boils at 212 °F, a 180-degree span. Celsius, introduced by Anders Celsius in 1742, simplified this by putting 0 at water's freezing point and 100 at its boiling point (at sea level), giving the convenient 100-degree span that made it the world's standard for everyday and scientific use. Kelvin, proposed by Lord Kelvin in 1848, keeps the Celsius degree size but shifts the zero all the way down to absolute zero — the coldest temperature physically possible, where molecular motion stops — which is why it never uses negative numbers.

Which Scale Is Used Where

In daily life the split is largely geographic: the United States (along with a few territories) uses Fahrenheit for weather, cooking, and body temperature, while almost every other country uses Celsius. That divide is the single biggest reason people reach for a converter — translating a recipe, a forecast, or a fever reading across the two systems. Kelvin is the scale of science: physics, chemistry, and engineering use it for gas laws, thermodynamics, and anything involving absolute temperature, because calculations that multiply or divide temperature only work from an absolute zero. Rankine plays the same absolute role in a handful of US engineering fields, pairing Fahrenheit-sized degrees with an absolute-zero starting point. Knowing which scale a number is in — and what it is being used for — is half the battle; the converter handles the arithmetic once you do.