Temperature Calculator

Q: What temperature scales does this calculator support?

This calculator converts between five scales: Celsius (°C) , Fahrenheit (°F) , Kelvin (K) , Rankine (°R) , and Réaumur (°Ré) . Enter a value in any one scale and get all four others instantly.

Q: How do I enter a negative temperature?

Click the ± button next to the input box. It will add or remove the minus sign for you. You can also type a minus sign directly before your number.

Q: What is absolute zero and why can't I go below it?

Absolute zero is −273.15°C (or 0 K). It is the coldest anything can ever be. At this point, atoms have almost no energy. No real temperature can go lower, so the calculator will show an error if you try.

Q: What does the Use button do on each result row?

The Use button takes that result value and puts it back into the input box with its scale selected. This lets you quickly reverse a conversion or chain multiple conversions without retyping.

Q: How accurate are the results?

Results are rounded to four decimal places . This is more than enough precision for school work, cooking, weather, and most science and engineering tasks.

Q: Can I copy a result to my clipboard?

Yes. Click the copy icon next to any result row. The value and its unit will be copied. A small "Copied!" message will appear to confirm it worked.

Q: What is the thermometer graphic showing me?

The thermometer gives you a visual picture of your temperature. It fills up higher for hotter values and changes color from blue (cold) to green (comfortable) to red (very hot). It covers a range of −50°C to 150°C.

Q: What is the largest value I can enter?

The calculator accepts temperatures up to ±1,000,000°C (or the equivalent in other scales). Values beyond that limit will show an error.

Temperature Calculator

Updated Jul 21, 2026 By Jehan Wadia

Introduction

This free temperature calculator lets you convert between Celsius, Fahrenheit, Kelvin, Rankine, and Réaumur in seconds. Just type a number, pick your starting scale, and get all four other values right away. The tool also shows a step-by-step solution so you can see exactly how each conversion works.

Temperature conversion is useful in science class, cooking, travel, and everyday life. For example, if a recipe says 350°F and your oven uses Celsius, our Fahrenheit to Celsius calculator or this all-in-one tool gives you the answer fast. Or if you study physics and need to work in Kelvin for an ideal gas law calculation, you can switch between scales with one click.

The built-in thermometer gives you a visual sense of how hot or cold your value is. A reference table of common temperatures is included at the bottom so you can quickly compare well-known points like the freezing and boiling points of water, body temperature, and absolute zero.

How to Use Our Temperature Calculator

Enter a temperature value and pick its scale. The calculator will instantly convert it to Celsius, Fahrenheit, Kelvin, Rankine, and Réaumur and show all five results.

Temperature Value: Type the number you want to convert into the input box. Use the ± button if your number is negative.

Input Scale: Pick the scale your number is in. Choose from Celsius (°C), Fahrenheit (°F), Kelvin (K), Rankine (°R), or Réaumur (°Ré).

Calculate: Press the Calculate button to see your temperature converted to all five scales at once. You can also click a Quick Reference Preset to load a common temperature like body temp or the boiling point of water.

How to Convert Temperatures Between Scales

Temperature tells us how hot or cold something is. Scientists and people around the world use different scales to measure it. The five main temperature scales are Celsius, Fahrenheit, Kelvin, Rankine, and Réaumur. This calculator lets you convert a temperature from any one of these scales to all the others instantly.

The Five Temperature Scales

Celsius (°C) is the most common scale in the world. Water freezes at 0°C and boils at 100°C. Most countries use Celsius for weather, cooking, and science.

Fahrenheit (°F) is used mainly in the United States. On this scale, water freezes at 32°F and boils at 212°F. The gap between freezing and boiling is 180 degrees, which makes each Fahrenheit degree smaller than a Celsius degree. If you only need to go between these two scales, try our dedicated Celsius to Fahrenheit calculator.

Kelvin (K) is the scale used in physics and chemistry. It starts at absolute zero, the coldest possible temperature, where all particle motion stops. Absolute zero is 0 K, which equals −273.15°C. Kelvin uses the same size degree as Celsius, just shifted down. You will never see a negative Kelvin value because nothing can be colder than absolute zero. Kelvin is essential when working with equations like the ideal gas law or when studying kinetic energy at the molecular level.

Rankine (°R) also starts at absolute zero, but it uses the same size degree as Fahrenheit. Engineers in the United States sometimes use it in thermodynamics calculations, such as when figuring out thermal expansion in structural materials. Absolute zero is 0°R, which equals −459.67°F.

Réaumur (°Ré) is an older scale rarely used today. Water freezes at 0°Ré and boils at 80°Ré. It was once popular in parts of Europe.

Key Temperature Conversion Formulas

Every conversion in this calculator runs through Celsius as a base. Here are the core formulas:

Celsius to Fahrenheit: °F = °C × 9/5 + 32
Fahrenheit to Celsius: °C = (°F − 32) × 5/9
Celsius to Kelvin: K = °C + 273.15
Celsius to Rankine: °R = (°C + 273.15) × 9/5
Celsius to Réaumur: °Ré = °C × 4/5

Temperatures Worth Knowing

Absolute zero (−273.15°C) is the lowest temperature that can exist. At this point, atoms have almost no energy left to give. 0°C (32°F) is when water turns to ice. 37°C (98.6°F) is normal human body temperature. 100°C (212°F) is when water boils at standard air pressure. These reference points help you quickly judge whether a temperature is cold, comfortable, or dangerously hot. For weather-related temperature effects, you may also find our wind chill calculator, heat index calculator, and dew point calculator useful.

Formulas used

Fahrenheit to Celsius

{}^{\circ}\mathrm{C} = ({}^{\circ}\mathrm{F} - 32) \times \frac{5}{9}

Kelvin to Celsius

{}^{\circ}\mathrm{C} = \mathrm{K} - 273.15

Rankine to Celsius

{}^{\circ}\mathrm{C} = ({}^{\circ}\mathrm{R} - 491.67) \times \frac{5}{9}

Réaumur to Celsius

{}^{\circ}\mathrm{C} = {}^{\circ}\mathrm{R\acute{e}} \times \frac{5}{4}

Celsius to Fahrenheit

{}^{\circ}\mathrm{F} = {}^{\circ}\mathrm{C} \times \frac{9}{5} + 32

Celsius to Kelvin

\mathrm{K} = {}^{\circ}\mathrm{C} + 273.15

Celsius to Rankine

{}^{\circ}\mathrm{R} = ({}^{\circ}\mathrm{C} + 273.15) \times \frac{9}{5}

Celsius to Réaumur

{}^{\circ}\mathrm{R\acute{e}} = {}^{\circ}\mathrm{C} \times \frac{4}{5}

Frequently asked questions

What temperature scales does this calculator support?

This calculator converts between five scales: Celsius (°C), Fahrenheit (°F), Kelvin (K), Rankine (°R), and Réaumur (°Ré). Enter a value in any one scale and get all four others instantly.

How do I enter a negative temperature?

Click the ± button next to the input box. It will add or remove the minus sign for you. You can also type a minus sign directly before your number.

What is absolute zero and why can't I go below it?

Absolute zero is −273.15°C (or 0 K). It is the coldest anything can ever be. At this point, atoms have almost no energy. No real temperature can go lower, so the calculator will show an error if you try.

Why does the calculator use Celsius as a base for all conversions?

Every scale can be converted to and from Celsius with a simple formula. By converting your input to Celsius first, the calculator only needs one set of formulas to reach all other scales. The math is the same either way.

What does the Use button do on each result row?

The Use button takes that result value and puts it back into the input box with its scale selected. This lets you quickly reverse a conversion or chain multiple conversions without retyping.

How accurate are the results?

Results are rounded to four decimal places. This is more than enough precision for school work, cooking, weather, and most science and engineering tasks.

Can I copy a result to my clipboard?

Yes. Click the copy icon next to any result row. The value and its unit will be copied. A small "Copied!" message will appear to confirm it worked.

What do the Quick Reference Presets do?

They fill in a well-known temperature for you with one click. Options include absolute zero, water freezing, room temperature, body temperature, and water boiling. All presets are in Celsius.

What is the thermometer graphic showing me?

The thermometer gives you a visual picture of your temperature. It fills up higher for hotter values and changes color from blue (cold) to green (comfortable) to red (very hot). It covers a range of −50°C to 150°C.

What is the largest value I can enter?

The calculator accepts temperatures up to ±1,000,000°C (or the equivalent in other scales). Values beyond that limit will show an error.

When would I use Kelvin instead of Celsius?

Kelvin is used in physics and chemistry equations like the ideal gas law and thermal energy formulas. These equations need an absolute scale that starts at zero, not a relative one like Celsius.

When would I use Rankine?

Rankine is an absolute scale like Kelvin, but it uses Fahrenheit-sized degrees. Some engineers in the United States use it in thermodynamics and heat transfer calculations.

Is Réaumur still used today?

Réaumur is mostly historical. It was once common in parts of Europe. Today it is rarely used outside of some older European recipes and historical science texts.

How do I read the step-by-step solution?

The step-by-step section shows each formula used, with your numbers plugged in. Step 1 identifies your input. The next steps show the math to convert to each scale, one at a time. Bold numbers are the final answers.

What does the reference table at the bottom show?

It lists common temperatures in both Celsius and Fahrenheit, from absolute zero up to 1,000°C. The row closest to your current input is highlighted in green so you can compare your value to familiar points.

Does this calculator work on phones?

Yes. The layout adjusts to fit smaller screens. The input, buttons, results, and thermometer all resize so you can use the tool on any phone, tablet, or computer.

Do I need to press Calculate every time?

No. The calculator updates automatically as you type or change the scale. The Calculate button is there if you prefer to click it, but results appear in real time.

At what temperature are Celsius and Fahrenheit equal?

Celsius and Fahrenheit are the same at −40 degrees. That means −40°C = −40°F. You can verify this by entering −40 in either scale.

Rate this calculator