Absolute zero
Absolute zero is the lowest temperature permitted by thermodynamics, where a system has the least thermal energy available to it.
How big is it?
0 K
Also -459.7 °F
Temperature · approximate
A little perspective
Absolute zero is 2.725 K cooler than Cosmic microwave background.
Cosmic microwave background: The cosmic microwave background is faint thermal radiation filling the universe, left over from the early stages after the Big Bang.
Measurements, assumptions & sources +
Absolute zero
The zero of the thermodynamic kelvin scale. It is approached in experiments, not reached by ordinary finite cooling.
NIST — 2022 CODATA fundamental constants
The marked temperature is calibrated. Unmeasured illustration details are representative.
Cosmic microwave background
The temperature of the nearly blackbody relic radiation. It is not the temperature of every object in space.
The marked temperature is calibrated. Unmeasured illustration details are representative.
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Why this measurement?
Why we use 0 K
For comparison, this page uses temperature. This is labelled approximate; the central value is useful for comparison, while real values or measurement solutions can vary.
The zero of the thermodynamic kelvin scale. It is approached in experiments, not reached by ordinary finite cooling.
The identifying illustration and the numerical comparison remain separate. How calibrated comparisons work →
Recorded properties
Absolute zero dimensions and measurements
| Property | Selected value | Recorded range | Basis |
|---|---|---|---|
| 0 K | Not recorded | approximate |
Around this scale
Go smaller. Go bigger.
These links use compatible temperature records, ordered around the selected value.
Around the same scale · TemperatureSuperfluid helium lambda point2.17 KThe superfluid helium lambda point is the temperature at which helium-4 transitions from a normal liquid to a superfluid state.Nearest higher value · TemperatureUltracold atom cloud1 × 10⁻⁷ KAn ultracold atom cloud is a collection of atoms cooled to temperatures near absolute zero, used in advanced physics experiments.Sources and method
Want to check the number?
The source records and measurement method remain available for inspection.
- NIST — 2022 CODATA fundamental constantsRecommended constants with uncertainties; exact SI definitions are distinguished from measured constants.
More ways to see it
Curated comparisons
There’s always another scale
Follow your curiosity.
TemperatureRoom temperature20 °CRoom temperature describes indoor air conditions generally considered comfortable for people and suitable for ordinary activities.
SpaceSun1,391,000 kmThe Sun is the star at the centre of the Solar System.
Fundamental physicsPlanck temperature1.417 × 10³² KThe Planck temperature is a theoretical temperature scale at which quantum gravitational effects are expected to become important.
TemperatureCosmic microwave background2.725 KThe cosmic microwave background is faint thermal radiation filling the universe, left over from the early stages after the Big Bang.TemperatureBoiling helium4.22 KBoiling helium is helium in its liquid state at its normal boiling point under standard atmospheric pressure.TemperatureUltracold atom cloud1 × 10⁻⁷ KAn ultracold atom cloud is a collection of atoms cooled to temperatures near absolute zero, used in advanced physics experiments.TemperatureSuperfluid helium lambda point2.17 KThe superfluid helium lambda point is the temperature at which helium-4 transitions from a normal liquid to a superfluid state.TemperatureHydrogen normal boiling point20.27 KHydrogen normal boiling point is the temperature at which hydrogen changes from a liquid to a gas at standard atmospheric pressure.