Temperature Converter

How to Convert a Temperature

Features

The Weather Rose 10 Degrees — Which 10?

Run "10°C" through the ordinary Celsius-to-Fahrenheit formula and you get 50°F, which is correct if 10°C is a reading — a cold morning. It is nonsense if 10°C is a change — the weather warming up by 10 degrees over the afternoon. A 10°C rise is actually an 18°F rise, because a change in temperature only cares about the size of the degree, not where either scale calls zero. Mix those two questions up — and it is a genuinely easy mix-up — and a number that looks perfectly reasonable is simply wrong. That distinction is unusual enough among unit converters that this one builds it in directly: a switch labelled Convert a Temperature Change (Δ) that strips the offset out of the maths the moment you flip it on, rather than leaving you to remember which formula applies to which kind of number.

Four Zeros That Refuse to Agree

Length and weight convert by plain multiplication because every unit involved shares a zero — zero metres is zero feet, no exceptions. Temperature scales don't extend that courtesy. Celsius puts zero at the freezing point of water. Fahrenheit puts it at a specific brine-and-ice mixture that has nothing to do with water freezing at all. Kelvin puts it at absolute zero, the coldest a system can physically be. None of the three agree, which is exactly why °F = (°C × 9⁄5) + 32 needs both a multiplication and an addition, and why skipping the addition — a surprisingly common shortcut — produces an answer that is wrong by exactly 32 degrees every time. This tool runs the full offset-and-scale formula for all 56 possible pairings across its 8 scales, chained through Kelvin internally so the result is identical no matter which two scales are actually selected. One small convention worth knowing: Kelvin never takes a degree symbol. It is written "310 K", never "310°K", because Kelvin is defined as an absolute unit of measurement rather than a degree offset from an arbitrary zero — a distinction this tool follows consistently throughout.

An Oven Dial, a Fever, and a Long-Haul Flight

A recipe from a US food blog wants the oven at 350°F, but the dial in front of you only shows Celsius — convert once and 176.7°C tells you exactly where to turn the knob. A digital thermometer reads 101.3°F while the rest of a family's medical history is in Celsius; converted, that's 38.5°C, and flipping on Δ mode afterward shows that a further 1°F rise from there is only 0.56°C, useful context for describing a change to a doctor over the phone rather than an absolute number. And two friends on a video call comparing weather — one watching 95°F on a US app, the other looking at 35°C in Sydney — settle the "who has it worse" argument in the time it takes to type one number into the From field. It is worth asking, in passing, why Fahrenheit is still the one showing up on that US weather app at all — it predates Celsius by roughly two decades and was already the default for American forecasts and home thermostats by the time most of the world standardised on Celsius through the 20th century, and the US never mandated a full switch for everyday use the way it did for scientific and medical measurement.

A Very Short Menagerie of Dead Scales

Celsius, Fahrenheit, and Kelvin cover almost every real use, but this converter keeps four more around for the sake of completeness — and because they are genuinely interesting. Rankine is still alive in some US thermodynamics and aerospace work: an absolute scale, like Kelvin, but built from Fahrenheit-sized degrees instead. Réaumur, which puts water's freezing point at 0° and boiling at 80°, quietly survives in a handful of older European pastry and cheese recipes. Delisle, used in 18th-century Russia, runs backwards — 0°De is boiling, and it gets colder as the number climbs. And Rømer, dated to 1701, is historically notable for a reason that has nothing to do with weather: it is the scale Ole Rømer was using when he made the first real estimate of the speed of light, timing the eclipses of Jupiter's moons against seasonal temperature notes. Even Celsius itself has a twist worth knowing: Anders Celsius's original 1742 scale ran backwards from the one carrying his name today — he set 0° at boiling and 100° at freezing. It was flipped to the familiar orientation within a few years of his death, by other scientists working from his instruments, and the reversed version is the one that stuck for good.

Reading the Thermometer

The bar under the main result is a quick visual anchor, not just decoration — it places the current reading somewhere between −50°C and 200°C so a converted number has an immediate gut-check before you trust it. The landmark buttons above it (Absolute Zero, Water Freezes, Room Temp, Body Temp, Water Boils, Oven Bake) jump straight to a known reference point in whatever scale is selected, which is a genuinely fast way to build a feel for an unfamiliar scale like Rankine or Réaumur — see where body temperature actually lands on it, rather than trying to memorise a formula. Precision sits alongside both: Auto keeps everyday numbers short and readable, while a fixed 1, 2, 4, or 6 decimal-place setting is there for the moment a lab report or engineering spec needs one consistent format rather than whatever looks tidy. All 8 scales sit in both the From and To dropdowns regardless of how obscure they are, deliberately — there is no separate "advanced" mode to dig through, because the whole point of a thermometer bar and a set of landmark buttons is to make an unfamiliar scale feel immediately orientable rather than gated behind extra clicks.

What This Thermometer Won't Measure

This is a scale-to-scale converter and nothing more — it does not compute heat index, wind chill, or dew point, all of which mix temperature with humidity and wind speed through separate meteorological formulas, and it says nothing about heat energy in joules, a different physical quantity entirely. As with everything else on this page, nothing typed here is sent anywhere: the arithmetic runs as plain JavaScript inside the browser tab, with no server call and no log, which matters for an industrial process temperature or an unpublished lab result. And for anything with real safety or regulatory weight — clinical readings, calibration certificates, process control — treat the output as a fast reference and confirm it against calibrated equipment rather than the final word. It also has nothing to say about how quickly a temperature changes over time — a cooling curve on a manufacturing line or a fever's rate of onset is a rate, not a single value, and needs different instrumentation entirely to capture properly. If gas or wind speed is part of the same problem, the Speed Converter picks up where this one stops, and the Pressure Converter covers the other half of most thermodynamics work.