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Kelvin Temperature Converter

Convert to and from Kelvin with our scientific temperature calculator. Essential for physics, chemistry, and thermodynamics.

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Body Temperature

Convert normal human body temperature from Celsius to Fahrenheit

Key values: 37 °C · to °F · = 98.6 °F

Baking Conversion

Convert a common baking temperature from Fahrenheit to Celsius

Key values: 350 °F · to °C · = 176.67 °C

Absolute Zero

Convert absolute zero from Kelvin to Celsius

Key values: 0 K · to °C · = -273.15 °C

Documentation

The Kelvin Scale

Kelvin is the SI unit of temperature. It uses the same degree size as Celsius but starts at absolute zero — the lowest physically possible temperature:

K = C + 273.15

K = \frac{5}{9}(F - 32) + 273.15

Note: Kelvin has no degree symbol. Write 300 K, not 300°K.

Absolute Zero

0 \text{ K} = -273.15°\text{C} = -459.67°\text{F}

At absolute zero, particles have minimum possible energy (quantum zero-point energy). The third law of thermodynamics states that absolute zero can be approached but never reached. The closest achieved in laboratories is about $10^{-10}$ K.

Key Temperatures in Kelvin

Event	Kelvin	Celsius
Absolute zero	0 K	−273.15°C
Liquid helium boils	4.2 K	−268.95°C
Liquid nitrogen boils	77 K	−196°C
Water freezes	273.15 K	0°C
Room temperature	293 K	20°C
Water boils	373.15 K	100°C
Sun's surface	5,778 K	5,505°C

Why Science Uses Kelvin

Proportional relationships require absolute scales. The ideal gas law $PV = nRT$ only works with absolute temperature. Doubling the Kelvin temperature doubles the pressure (at constant volume). Doubling Celsius doesn't mean twice the thermal energy — 20°C is not “twice as hot” as 10°C. But 600 K is twice the thermal energy of 300 K.

Color Temperature

Light bulbs and displays are rated in Kelvin to describe their color warmth:

2700 K — Warm white (incandescent bulb)
4000 K — Neutral white (office lighting)
5500 K — Daylight (noon sun)
6500 K — Cool daylight (overcast sky, monitor default)

This is the temperature a theoretical black body would need to glow that color. Lower Kelvin = warmer (more red/yellow); higher Kelvin = cooler (more blue).

Frequently Asked Questions

How do I convert Celsius to Kelvin?

Add 273.15 to the Celsius temperature. The formula is $K = C + 273.15$ . For example, $20^\circ C = 293.15 \text{ K}$ . Kelvin uses the same degree size as Celsius but starts at absolute zero.

What is absolute zero?

Absolute zero is $0 \text{ K}$ ( $-273.15^\circ C$ or $-459.67^\circ F$ ), the lowest physically possible temperature. At this point, particles have minimum possible energy. The third law of thermodynamics states it can be approached but never reached.

Why does Kelvin not use a degree symbol?

The Kelvin scale is an absolute thermodynamic scale, not a relative one. By international convention, temperatures are written as 300 K, not $300^\circ K$ . This distinguishes it from Celsius and Fahrenheit, which are relative scales.

Why does science use Kelvin instead of Celsius?

Physical laws like the ideal gas law ( $PV = nRT$ ) require an absolute temperature scale. Doubling Kelvin means doubling thermal energy, but doubling Celsius does not. $600 \text{ K}$ is truly twice the thermal energy of $300 \text{ K}$ .

What is color temperature in Kelvin?

Color temperature describes the warmth of light. A 2700 K bulb produces warm white light, 4000 K is neutral white, 5500 K matches noon daylight, and 6500 K is cool daylight. Lower Kelvin means warmer (more yellow) light.