Temperature Converter

Celsius, Fahrenheit and Kelvin

Unlike length or weight, temperature scales do not share a common zero, so you cannot convert by multiplying alone. This tool uses the standard formulas — °F = °C × 9/5 + 32 and K = °C + 273.15 — to give exact conversions in both directions.

Enter a value in any scale and read it instantly in the other two, whether you are cooking, checking the weather, or doing science homework.

Common temperature conversions

• Celsius to Fahrenheit and Fahrenheit to Celsius
• Celsius to Kelvin for scientific work
• Body temperature, oven temperature and weather

Key features at a glance

• Converts between Celsius, Fahrenheit, and Kelvin
• Applies the correct affine formulas, not simple ratios
• Shows all three scales at once
• Handles negative temperatures correctly
• Instant, precise results as you type
• Runs entirely in your browser, even offline

Why temperature conversion is different

Most unit conversions are simple proportions — double the meters, double the feet. Temperature is different because its scales do not share a common zero point. Zero degrees Celsius and zero degrees Fahrenheit represent completely different temperatures, so you cannot convert by multiplying alone; you must also shift by an offset. This is why the formula to go from Celsius to Fahrenheit multiplies by 9/5 and then adds 32.

Mathematically, this is an affine relationship rather than a linear one, and getting it wrong is a classic mistake. The converter applies the exact formulas in both directions — °F = °C × 9/5 + 32, K = °C + 273.15, and their inverses — so the results are always correct, including for the negative temperatures where sign errors most often creep in.

The three scales and where they are used

Celsius, used in most of the world, sets 0° at the freezing point of water and 100° at its boiling point, which makes it intuitive for weather and cooking. Fahrenheit, used primarily in the United States, places freezing at 32° and boiling at 212°, giving finer gradations for everyday air temperatures without decimals.

Kelvin is the scientific scale, starting at absolute zero — the coldest possible temperature, where molecular motion stops — and using the same degree size as Celsius. Because it has no negative values, Kelvin is essential in physics and chemistry, where temperatures appear in equations that would break with a scale that goes below zero. Each scale suits its domain, which is why being able to move between them quickly is so useful.

Reference points worth memorizing

A few anchor points make temperature conversions intuitive. Water freezes at 0°C / 32°F / 273.15 K and boils at 100°C / 212°F / 373.15 K. Normal human body temperature is about 37°C or 98.6°F, and a comfortable room is roughly 20–22°C or 68–72°F. Knowing these lets you sanity-check any conversion at a glance.

The scales also meet at one curious point: −40 degrees is the same in both Celsius and Fahrenheit, because that is where the offset and ratio cancel out. Beyond trivia, that fact is a quick way to remember that the two scales cross, and it highlights why a reliable converter beats guessing — the relationship is not as simple as it first appears.

Tips for converting temperature

• Celsius to Fahrenheit: multiply by 9/5 and add 32
• For a rough estimate, double the Celsius value and add 30
• Kelvin equals Celsius plus 273.15 — no multiplication needed
• Remember −40°C equals −40°F, where the scales meet
• Use Kelvin for any scientific calculation to avoid negative values

Why choose our temperature converter?

Our converter is completely free with no signup, no limits, and no subscription. It runs entirely in your browser, so conversions are instant, it works offline, and the values you enter never leave your device.

It is one of more than 200 free tools on ToopTools, and you can pin it to your My Workspace, a personalized workspace where you keep the tools you use most in a single dashboard. Beside the other unit converters, it makes switching between temperature scales effortless.

Common use cases

People use the temperature converter when following recipes that give oven temperatures in an unfamiliar scale, when checking the weather while traveling, and when doing science homework that requires Kelvin. It removes the offset-and-ratio math that trips so many people up.

Cooks convert oven settings between Celsius and Fahrenheit, travelers translate forecasts, and students and scientists move between Celsius and Kelvin for calculations. Because all three scales appear at once, you immediately see a temperature in whichever form your task needs.

Is the temperature converter free?

Yes. It is completely free with no account, no sign-up, and no usage limits. Convert as many temperatures as you like at no cost.

How do I convert Celsius to Fahrenheit?

Multiply the Celsius value by 9/5 and add 32. For example, 20°C × 9/5 + 32 = 68°F. A rough shortcut is to double the Celsius figure and add 30, which gets you close.

Why can't I just multiply to convert temperature?

Because temperature scales have different zero points, so conversion requires both a ratio and an offset. Multiplying alone ignores the offset and gives a wrong answer; the correct formulas add or subtract the offset as well.

What is absolute zero?

Absolute zero is the lowest possible temperature, 0 Kelvin, equal to −273.15°C. At that point molecular motion is at its minimum. The Kelvin scale starts here, which is why it never has negative values.

At what temperature do Celsius and Fahrenheit match?

At −40 degrees. Minus forty is the same on both scales, because that is the single point where the offset and ratio between them cancel out. It is a handy fact for checking conversions.

Are my conversions kept private?

Yes. Everything is computed in your browser and nothing is uploaded, so the values you enter stay private and the tool works without an internet connection.

How do I convert Fahrenheit to Celsius?

Enter the temperature in Fahrenheit and select Celsius as the target, and the converter applies the formula (°F − 32) × 5/9 to show the result instantly. It also handles Kelvin, so you can move between all three temperature scales in one step.

Does the temperature converter work offline?

Yes. The conversion runs entirely in your browser, so once the page has loaded the tool works without an internet connection, and nothing you enter is uploaded — it stays private on your own device.