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Kelvin to Fahrenheit Converter

Convert Kelvin to Fahrenheit with our free Kelvin to Fahrenheit converter — or switch between Kelvin, Celsius, Fahrenheit, and Rankine in any direction. 300 K equals 80.33°F, a warm summer day, and this page converts any temperature instantly.

Reference temperatures

How it works

Kelvin, Celsius, Fahrenheit, and Rankine are four scales for measuring the same thing — temperature — but they start at different points and use different sized degrees. Celsius sets 0 at the freezing point of water and 100 at its boiling point. Fahrenheit sets 32 at the freezing point and 212 at the boiling point, so a Fahrenheit degree is smaller than a Celsius degree. Kelvin starts at absolute zero, the lowest temperature physically possible, and uses Celsius-sized degrees. Rankine starts at absolute zero too, but uses Fahrenheit-sized degrees. This converter goes through Celsius as the common middle step, which keeps every combination exact.

The relationships between the scales are:

To convert Kelvin to Fahrenheit, first subtract 273.15 to get Celsius, then multiply by 9/5 and add 32. To convert Fahrenheit back to Kelvin, reverse the steps: subtract 32, multiply by 5/9 to get Celsius, then add 273.15. Celsius to Kelvin is a simple shift of 273.15, and Rankine is Kelvin multiplied by 9/5, since a Rankine degree is the same size as a Fahrenheit degree. Pick the "from" and "to" units in the converter above and it handles every combination, including converting a scale to itself.

Kelvin is the scale of science. Because it starts at absolute zero — 0 K, or −273.15°C — a temperature in Kelvin is directly proportional to the average energy of the particles in a substance, which makes the maths of physics, chemistry, and thermodynamics work cleanly. Gas laws, for example, only give correct answers in Kelvin: doubling the Kelvin temperature doubles the pressure of a gas at fixed volume, while doubling the Celsius temperature does nothing of the sort. That is why lab reports, weather models, and astronomy all use Kelvin, even when everyday conversation uses Celsius or Fahrenheit.

The number 273.15 is the bridge between Kelvin and Celsius, and it is worth remembering. Water freezes at 273.15 K and boils at 373.15 K; room temperature is about 293 K, and body temperature is about 310 K. A temperature like 300 K is therefore a warm day: 300 minus 273.15 is 26.85°C, and 26.85°C times 9/5 plus 32 is 80.33°F. The same 300 K in Rankine is 540°R, a number that looks large only because Rankine degrees are smaller.

Fahrenheit still rules everyday life in a few places, so converting between Kelvin and Fahrenheit usually means translating science into weather. A lab result of 310 K is body temperature, 98.6°F. A forecast of 273 K is freezing, 32°F. And a cryogenic temperature like 77 K — the boiling point of liquid nitrogen — is −196.15°C, or −320.98°F, cold enough to freeze almost anything it touches. The converter handles negative Celsius and Fahrenheit values freely, but Kelvin and Rankine can never go below zero: a result below 0 K means the input was impossible, and the calculator will say so.

Worked example

A science student reads that a reaction runs at 300 K and wants to know what that is in Fahrenheit.

Step 1: Write down the temperature — 300 K.
Step 2: Convert Kelvin to Celsius — 300 − 273.15 = 26.85°C.
Step 3: Convert Celsius to Fahrenheit — 26.85 × 9/5 + 32 = 48.33 + 32 = 80.33.
Step 4: Round to two decimal places — 80.33°F.

That is the exact result this converter gives for 300 K: 80.33°F, a warm summer afternoon. Two checks confirm the method: 0°C converts to 32°F, the freezing point of water, and 273.15 K converts to the same 32°F, since 273.15 K is exactly 0°C. Going the other way, 100°F converts to Celsius by (100 − 32) × 5/9 = 37.78°C, and adding 273.15 gives 310.93 K — just above body temperature.

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