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Temperature Converter: Celsius, Fahrenheit, and Kelvin

Convert any temperature between °C, °F, and K instantly. All three values update at once with the exact formula shown.

This temperature converter shows Celsius, Fahrenheit, and Kelvin simultaneously. Type a value in any field and the other two update instantly with the exact formula used. Useful for weather comparisons between countries that use different scales, converting recipe oven temperatures, reading scientific data in Kelvin, or checking medical temperature references. The converter validates against absolute zero so it catches inputs that are physically impossible.

Frequently asked questions

  • How do you convert Celsius to Fahrenheit?

    Multiply the Celsius temperature by 9/5 (or 1.8) and add 32. The formula is °F = (°C × 9/5) + 32. For example, 100°C equals (100 × 1.8) + 32 = 212°F.

  • How do you convert Fahrenheit to Celsius?

    Subtract 32 from the Fahrenheit temperature, then multiply by 5/9. The formula is °C = (°F − 32) × 5/9. For example, 98.6°F equals (98.6 − 32) × 5/9 = 37°C.

  • What temperature is the same in Celsius and Fahrenheit?

    -40 degrees is the only point where Celsius and Fahrenheit show the same number. At −40°C = −40°F, the two scales intersect.

  • What is 37 degrees Celsius in Fahrenheit?

    37°C equals 98.6°F. This is normal human body temperature. Using the formula: (37 × 9/5) + 32 = 66.6 + 32 = 98.6°F.

  • What is Kelvin and how is it different from Celsius?

    Kelvin is an absolute temperature scale that starts at absolute zero (0 K), the coldest possible temperature. One Kelvin degree is the same size as one Celsius degree, but Kelvin has no negative values. To convert Celsius to Kelvin, add 273.15. Water freezes at 273.15 K and boils at 373.15 K.

  • What is absolute zero in Celsius, Fahrenheit, and Kelvin?

    Absolute zero is 0 K, −273.15°C, or −459.67°F. This is the coldest possible temperature where all molecular motion stops.

  • What is the freezing and boiling point of water in all three scales?

    Water freezes at 0°C, 32°F, and 273.15 K. Water boils at 100°C, 212°F, and 373.15 K at standard atmospheric pressure.

  • How do you convert Fahrenheit to Kelvin?

    First convert Fahrenheit to Celsius by subtracting 32 and multiplying by 5/9, then add 273.15. The direct formula is K = (°F − 32) × 5/9 + 273.15.

Related tools

Three scales, one number

Weather reports in the US use Fahrenheit. Most of the rest of the world uses Celsius. Scientists use Kelvin. If you've ever read an oven temperature in a foreign recipe or checked the forecast for a trip, you've needed to switch.

Type a value into any of the three boxes and the other two update right away. The formula used is shown too, so you can do it by hand if you ever need to.

The formulas

Celsius to Fahrenheit: multiply by 9/5, then add 32. So 20 C is 68 F. Fahrenheit to Celsius: subtract 32, then multiply by 5/9. So 98.6 F gives 37 C, which is normal body temperature.

Kelvin is simple. Add 273.15 to Celsius. A Kelvin degree is the same size as a Celsius degree, only the zero point differs. 0 C is 273.15 K.

  • Water freezes at 0 C, 32 F, 273.15 K
  • Water boils at 100 C, 212 F, 373.15 K at sea level
  • Absolute zero is -273.15 C, -459.67 F, 0 K

A mental shortcut

For a rough Celsius to Fahrenheit guess, double the number and add 30. 20 C gives 70, close to the true 68. It drifts at extremes but it's fine for deciding on a jacket.

Here's a fun fact. At -40 degrees the Celsius and Fahrenheit scales agree. -40 C equals -40 F. It's the only point where they meet.

What Kelvin is for

Kelvin starts at absolute zero, the coldest anything can get, where particles have almost no motion. That makes it the natural scale for physics and chemistry, because there are no negative values, and formulas like the gas law work directly.

You don't say degrees with Kelvin. It's just 300 kelvin.

Real-life uses

Cooking is the big one. 350 F is about 175 C, and 400 F is about 200 C. Many ovens round, so being a few degrees off won't ruin dinner. Fever checks matter more: 100.4 F, or 38 C, is the usual line for fever in adults.

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Cooking, weather and fever

Oven dials are where most people hit this. A recipe from a British or Australian site may list Celsius or a gas mark, while your oven shows Fahrenheit. 180 degrees C is 356 F, and most ovens treat 350 as the match. That small gap rarely hurts a cake.

Weather is the other big one. Travelling from the US to Europe, a forecast of 25 means a warm summer day, and in Fahrenheit the same number means a cold coat day. Knowing a few anchors saves you.

Body temperature needs care. A normal reading sits near 37 C, or 98.6 F. A fever is usually counted from about 38 C, or 100.4 F. If the number worries you, call a doctor and don't rely on a converter.

Anchor points to remember

You don't need the formula every time. Memorize a handful and estimate between them.

  • 0 C is 32 F, the freezing point of water
  • 10 C is 50 F, a cool spring day
  • 20 C is 68 F, a comfortable room
  • 30 C is 86 F, properly hot
  • 100 C is 212 F, water boils at sea level

Where people slip

Negative values trip people up. -40 is the one place where Celsius and Fahrenheit meet, and it's a handy check on any formula you write. If your code gives anything else at -40, the formula is wrong.

Also watch for temperature differences. A change of 10 C is a change of 18 F, not 50 F. You only add the 32 when converting a reading, never when converting a gap between two readings.

Kelvin has no degree sign and no negatives. Treat it as a count from absolute zero.