Physics · Thermal radiation
Wien's displacement law calculator.
Enter a temperature to find where a blackbody radiates most strongly, or enter a peak wavelength to find the temperature.
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Wien's displacement law
The spectrum of an ideal blackbody peaks at a wavelength inversely proportional to its absolute temperature: λmax = b / T, where b = 2.897771955×10−3 m K (exact in the 2022 CODATA values). Hotter objects peak at shorter wavelengths.
Worked example. At T = 5800 K, λmax = 2.897771955×10−3 / 5800 = 499.6 nm, in the visible range. At 300 K (room temperature) the peak is 9659 nm, about 9.66 µm, in the infrared. Going the other way, a peak at 1000 nm means T = 2897.8 K.
The peak of a spectrum measured per unit frequency lands at a different place, so this law applies to the per-wavelength curve only.
Frequently asked questions
What is Wien's displacement law?
lambda_max = b / T. The wavelength where a blackbody emits most strongly is the constant b divided by the absolute temperature in kelvin.
What is the value of the Wien constant?
b = 2.897771955e-3 m K. NIST lists it as exact in the 2022 CODATA values.
Why does 300 K peak in the infrared?
At 300 K the formula gives about 9.66 micrometres, far longer than visible light (which is why room-temperature objects glow only in the infrared).
Can I use Celsius?
Enter kelvin. Convert from Celsius by adding 273.15. The result panel also shows the Celsius value.
Does this work for the Sun or a lamp?
It is a good approximation for objects that radiate like blackbodies, but real surfaces differ and the answer is a model value, not a measurement.
Sources
Checked
- NIST CODATA: Wien wavelength displacement law constant (exact, 2022 values)
- OpenStax University Physics Vol. 3: Key equations, ch. 6 (Wien displacement law)
NIST gives b = 2.897 771 955... x 10^-3 m K (exact); OpenStax gives the law as lambda_max T = 2.898 x 10^-3 m K. Examples are arithmetic on that constant, not measured temperatures. Runs entirely in your browser. Nothing you type is sent or stored.
Scope
Ideal blackbody model for study. Not a thermometer; do not use it for safety-critical temperature work.