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Scientific Tools · Updated October 21, 2026 · Reviewed by FormatFlow Editorial

Temperature Converter

You can convert a temperature between Celsius, Fahrenheit and Kelvin in your browser: choose the input unit, see all three scales at once, and follow the exact formula used for the conversion.

Runs in your browserFree · No sign-up · No watermark
TemperatureRuns in your browser
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Everything runs locally in this tab. No file is uploaded while the tool loads.

This tool runs in your tab. Nothing is uploaded and no copy is stored.

How files are handled

At a glance

Works with
Temperature
Processing
In your browser
Price
Free, no account
Updated
October 21, 2026
All Scientific Tools

About Temperature Converter

Temperature scales do not convert like lengths: Fahrenheit and Celsius have different zero points as well as different step sizes, and Kelvin has no degree symbol at all. That offset is why -40 is the one value where Celsius and Fahrenheit agree, and why a plain multiplication gives wrong results.

This converter applies the exact formulas F = C × 9/5 + 32 and K = C + 273.15, shows the working with your number substituted, and displays all three scales at once. Below absolute zero it refuses the value with an explanation, and a decimal-places control keeps output at a reporting precision that suits the measurement. Everything runs locally.

What this tool does

The details that matter when you use Temperature Converter for real work.

  • All three scales at once

    One input gives Celsius, Fahrenheit and Kelvin side by side, with the source unit highlighted.

  • Exact formulas shown

    The formulas and your number substituted into them appear under the results, so the offset and the 9/5 factor are visible.

  • Absolute-zero validation

    Values colder than 0 K are rejected with an explanation instead of producing an impossible conversion.

  • Rounding control

    Display 0 to 6 decimal places without changing the arithmetic, which always uses the exact 9/5 and 273.15 factors.

  • Example values

    Preset buttons fill in the -40 crossover, body temperature, freezing water and absolute zero for quick checks.

  • Reference points table

    A fixed table lists freezing, boiling, body temperature and absolute zero in all three scales.

How to use Temperature Converter

No account, no installation — the whole job happens in this browser tab.
  1. 01

    Choose the input unit

    Select Celsius, Fahrenheit or Kelvin for the temperature you are going to enter.

  2. 02

    Enter the temperature

    Type the number; decimals and negative values are accepted, but comma decimal marks are not.

  3. 03

    Read all three results

    Celsius, Fahrenheit and Kelvin are shown together, with your input unit highlighted.

  4. 04

    Check the formula

    The formulas and the substituted arithmetic sit under the results if you need to show your working.

  5. 05

    Set the display precision

    Pick the number of decimal places that suits the measurement before copying a result.

How this tool works

Works with
Temperature
Processing
Client-side, in your browser. Nothing is uploaded.
Requirements
Chrome, Edge, Firefox or Safari · JavaScript enabled

Limitations worth knowing

  • Only absolute temperatures are converted; a temperature difference follows different rules and is not supported here.
  • Values below absolute zero are rejected rather than converted, because they are physically impossible.
  • Results are rounded for display to the chosen decimal places, so they are reporting aids rather than instrument readings.

Privacy and file handling

The temperature you type is converted with plain JavaScript inside your browser tab. Nothing is uploaded, logged or stored, and no request is made to a server while you convert. Closing the page clears the input.

Read the full privacy policy

Temperature Converter FAQ

Short, direct answers to the questions people ask before using this tool.
How do I convert Celsius to Fahrenheit exactly?
Multiply by 9, divide by 5 and add 32, so F = C × 9/5 + 32. For 37 °C that gives 37 × 1.8 + 32 = 98.6 °F.
Why is -40 °C the same as -40 °F?
It is the one temperature where the two scales cross. Substituting -40 into F = C × 9/5 + 32 gives -72 + 32 = -40, so both scales read the same number.
How do I convert Kelvin to Celsius?
Subtract 273.15: C = K − 273.15. A sample at 300 K is therefore 26.85 °C, and 0 K equals -273.15 °C.
What is absolute zero in Fahrenheit?
Absolute zero is -459.67 °F, which is also -273.15 °C or 0 K. Below any of those values no temperature exists, so the converter rejects the input.
Does the converter round the results?
Only for display. Choose 0 to 6 decimal places for the numbers shown; the conversion itself uses the exact 9/5 and 273.15 factors before rounding.
Can I convert a temperature difference instead of a point?
This tool converts absolute temperatures, which include the offset. A temperature difference uses different rules — Fahrenheit degrees are 5/9 the size of Celsius degrees and Kelvin intervals match Celsius intervals — so do not simply subtract converted values.
Are comma decimal marks supported?
No. Inputs such as 98,6 are rejected because a comma is a thousands separator in some locales and a decimal mark in others; write 98.6 instead.
Do gas-law calculations need the Kelvin value?
Most gas-law and thermodynamics formulas use absolute temperature, so convert to kelvin by adding 273.15 to Celsius before substituting the value into the equation.

Background reading

Format guides that explain the trade-offs behind Temperature Converter.