Converter Tools

Temperature Converter

Convert temperatures between Celsius, Fahrenheit and Kelvin using the exact formulas, with absolute-zero validation. See the formula used. Fully offline.

Runs entirely in your browser — nothing you type is uploaded.

This tool runs in your browser. Please enable JavaScript to use it — the guide below explains what it does.

Note: the converter runs in your browser with JavaScript. With JavaScript off you can read this guide, but the controls will not appear.

Convert Celsius, Fahrenheit and Kelvin

This tool converts temperatures between the three common scales entirely in your browser using the exact formulas. Enter a temperature, choose the scales, and get a precise result — with the formula shown and a check that stops physically impossible values below absolute zero.

How it works

  1. Enter a temperature (negative values are allowed above absolute zero).
  2. Choose the From and To scales — Celsius, Fahrenheit or Kelvin.
  3. Click Convert to see the result and the formula used, or Swap to reverse.
  4. Copy the result or Reset to start again.

The formulas

  • Celsius → Fahrenheit: (°C × 9/5) + 32
  • Fahrenheit → Celsius: (°F − 32) × 5/9
  • Celsius → Kelvin: °C + 273.15
  • Kelvin → Celsius: K − 273.15
  • Fahrenheit ↔ Kelvin: converted via Celsius.

Reference points & absolute zero

Handy checkpoints: 0 °C = 32 °F = 273.15 K (water freezes), 100 °C = 212 °F (water boils at sea level), and −40 °C = −40 °F. Nothing can be colder than absolute zero (−273.15 °C, i.e. 0 K), so the tool rejects any value below that — including negative Kelvin — as physically impossible.

Examples

  • 37 °C ≈ 98.6 °F (body temperature)
  • 25 °C = 298.15 K (room temperature)
  • −40 °C = −40 °F

Privacy

Everything runs locally in your browser. The values you enter are never uploaded, stored or shared, and the tool makes no network requests.

Frequently Asked Questions

Which temperature scales are supported?
Celsius, Fahrenheit and Kelvin, in any direction. The tool shows the exact formula used for each conversion.
What formulas does it use?
Celsius to Fahrenheit is (°C × 9/5) + 32; Fahrenheit to Celsius is (°F − 32) × 5/9; Celsius to Kelvin is °C + 273.15; and Kelvin to Celsius is K − 273.15. Fahrenheit ↔ Kelvin conversions go through Celsius.
Does it check for impossible temperatures?
Yes. Nothing can be colder than absolute zero (−273.15 °C, which is 0 K), so any value below that — including negative Kelvin — is rejected as physically impossible. Negative Celsius and Fahrenheit values above absolute zero are allowed.
What are some known reference points?
0 °C = 32 °F = 273.15 K (water freezes), 100 °C = 212 °F (water boils at sea level), and −40 °C = −40 °F (where the two scales meet).
Is my data stored or sent anywhere?
No. All conversions run locally in your browser — the values you enter are never uploaded, saved or shared, and the tool makes no network requests.

Related Converter Tools tools

Currency Converter (Offline)

Convert between 16 common currencies using built-in approximate reference rates — completely offline. Reference rates, not live: always verify current rates before any transaction.

Converter Tools Open Tool

Length Converter

Convert length and distance between millimetres, centimetres, metres, kilometres, inches, feet, yards, miles and nautical miles. Accurate, instant and fully offline.

Converter Tools Open Tool

Weight Converter

Convert weight between milligrams, grams, kilograms, metric tons, ounces, pounds and stone. A simple everyday weight converter using precise mass-unit factors. Fully offline.

Converter Tools Open Tool
Scroll to Top