Second radiation constant = 1.438 776 877... × 10−2 m·K

Value
1.438 776 877... × 10−2
Unit
m·K
Uncertainty
exact (by definition)
Copy-ready
1.438776877e-2

The second radiation constant c₂ = hc/k, the constant in the exponent of Planck's law.

Used with c₁ in Planck's law; infrared thermometers and the ITS-90 temperature scale rely on it.

NIST, Fundamental Physical Constants — Complete Listing (2022 CODATA adjustment), retrieved 2026-07-26.

Electrical, thermal and X-ray constants

Angstrom starConductance quantumCopper x unitElectron charge to mass quotientFermi coupling constantFirst radiation constantHartree energyJosephson constantLattice parameter of siliconLattice spacing of ideal Si (220)Loschmidt constant (273.15 K, 101.325 kPa)Magnetic flux quantumMolar mass constantMolar mass of carbon-12Molar Planck constantMolar volume of siliconMolybdenum x unitNeutron-proton mass differenceProton charge to mass quotientQuantum of circulationSackur-Tetrode constant (1 K, 101.325 kPa)Second radiation constantVon Klitzing constantWeak mixing angleWien frequency displacement law constantW to Z mass ratio

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All physical constants

Constants and formula sheetElectrical, thermal and X-ray constantsAll calculators