Temperature Converter

Convert a temperature between five scales, or print one reading on all of them at once.

Runs on your deviceConvertersWorkingNo account needed

What this tool does

Temperature Converter turns a reading on one scale into the same reading on another, across Celsius, Fahrenheit, Kelvin, Rankine and Réaumur. The From and To dropdowns set the pair, but any line may carry its own units and override them — type 20 c to f, or 300 K to °C, and that line is converted on its own terms. Full names are accepted alongside the symbols — celsius, kelvin, rankine and reaumur all resolve, as does a deg prefix with or without a space — so a pasted column of mixed readings converts without being tidied up first.

The one thing worth understanding before you trust an answer is what the number means. These scales are affine: they differ in where zero sits as well as in the size of a degree, so the tool converts a point on a scale and never a difference between two points. Ask for 10 °C in Fahrenheit and it answers 50 °F, because ten degrees Celsius is that temperature. It is not saying that a rise of ten Celsius degrees is a rise of fifty — that rise is 18 Fahrenheit degrees, and getting it means converting both endpoints and subtracting the results yourself.

Nothing about a conversion leaves this tab. The five scales and the arithmetic that walks between them ship with the page, so the readings you type are never sent anywhere and the tool still answers with the network unplugged. Readings below absolute zero are refused rather than quietly converted, and the error names the floor for the scale you used — enter −300 °C and it replies with −273.15 °C. That refusal stops the whole run rather than the offending line, so a pasted column with one impossible reading in it comes back as an error and not as a partial table. Precision controls the rounding: automatic keeps up to ten significant figures with trailing zeros trimmed, and the fixed settings round to a set number of decimals.

How to use it

  1. Enter the readings, one to a line. 100, -40 °F, 300 K to °C and 98.6 F to C are all understood, so a column copied out of a spreadsheet converts in one pass.
  2. Pick the From and To scales. They apply to every line that does not name its own units. Setting To to All units instead prints the value on all five scales, each with its symbol and full name.
  3. Choose the precision. Automatic keeps up to ten significant figures. The fixed settings round to 0, 1, 2, 3, 4, 6 or 8 decimals, which is what you want when the output goes into a table.
  4. Read the result, or take the table. Each line comes back as "100 °C = 212 °F", with a table view beside it and the conversion formula printed under the last result.

Processing & privacy

Runs on your device. Your file is processed directly in this browser.

Common use cases

Following a recipe written for another oven

American recipes give Fahrenheit and a European dial is marked in Celsius. 350 F to C settles the number before the tin goes in.

Reading a thermometer bought abroad

A device that only shows Fahrenheit is hard to judge by instinct. 98.6 °F comes back as exactly 37 °C rather than the rounded figure on a wall chart.

Converting a logged column of readings

Paste a sensor or weather-station export straight in. Lines convert in the order they arrive, a list of several hundred reports its progress as it goes and can be cancelled part-way, and one impossible reading fails the batch rather than being skipped over.

Working in Kelvin or Rankine

Physics coursework is written in Kelvin and some US engineering tables still use Rankine. Both convert directly to and from the everyday scales.

Questions

Is anything uploaded?
No. Temperature Converter runs as JavaScript inside this tab, so the values you type stay on your device and are not transmitted, logged or stored. Once the page has loaded it works offline.
Can it convert a temperature difference?
No — this is the misreading to watch for. Every conversion treats the number as a point on a scale, so 10 °C becomes 50 °F. A rise of 10 Celsius degrees is a rise of 18 Fahrenheit degrees; to get that, convert both endpoints and subtract the two results.
Why was my value rejected?
Anything below absolute zero is refused, because no scale has a reading beneath it. The error names the floor in the units you typed: −273.15 °C, −459.67 °F, 0 K, 0 °R or −218.52 °Ré. A line that does not begin with a number is refused as well, quoted back with its line number. Either refusal ends the whole run, so fix the line and convert again.
Do I have to use the dropdowns?
No. A unit typed after the number overrides the From box, and "to" followed by a unit overrides the To box. Bare letters work as well as symbols, so 20 c to f, 98.6 F to C and 300 K to °C are all valid lines. One spelling it will not take is degrees C written out in full; deg C and degC both work.
Why does the formula line sometimes not appear?
It is written out for the common pairs only: Celsius, Fahrenheit and Kelvin against one another, Fahrenheit and Kelvin against Rankine, and Celsius against Réaumur. Celsius to Rankine still converts correctly — it simply prints without a formula beneath it. An All units table has no single pair to describe, so it carries no formula either.
How is this different from the Unit Converter?
Unit Converter covers ten quantities behind a Quantity dropdown and shares these same tables. This page is the temperature half with the choice already made, so there is one fewer setting between you and the answer.

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