Wien's Law Calculator
Enter an absolute temperature in kelvin to get the peak emission wavelength of a blackbody — in metres and nanometres — and see why hotter objects glow at shorter wavelengths.
Peak wavelength in two units
Enter the temperature and this Wien's law calculator returns the peak wavelength (b ÷ T) in metres and the same value in nanometres together.
Use kelvin
Wien's law needs an absolute temperature — add 273.15 to a Celsius value to get kelvin before you start.
What is Wien's displacement law?
The colour of a glowing object
Wien's displacement law tells you the wavelength at which a hot object — an ideal blackbody — emits the most light. That peak wavelength is inversely proportional to the object's absolute temperature, so the hotter the object, the shorter the wavelength and the bluer the glow. This Wien's law calculator turns a single measurement, the temperature in kelvin, into the peak wavelength in both metres and nanometres. It is the number behind a star's colour, the warm glow of a heated filament, and the way an electric ring shifts from dull red to bright orange as it warms.
Enter an absolute temperature in kelvin to get the peak emission wavelength in metres and nanometres instantly.
The peak wavelength is the Wien displacement constant divided by the absolute temperature, and the nanometre value is just that wavelength multiplied by one billion.
λ_max = b ÷ TThe constant b = 2.897771955 × 10⁻³ m·K is fixed, so temperature does all the work: because it sits in the denominator, doubling the temperature halves the peak wavelength. Use kelvin for the temperature and the wavelength comes back in metres, which the calculator also converts to the more readable nanometres.
Suppose you want the peak wavelength of the Sun, whose surface is about 5772 K.
Take the constant
b = 2.897771955 × 10⁻³ m·K — the Wien displacement constant.
Divide by the temperature
2.897771955 × 10⁻³ ÷ 5772 ≈ 5.02 × 10⁻⁷ m — the peak wavelength in metres.
Convert to nanometres
5.02 × 10⁻⁷ m × 10⁹ ≈ 502 nm — green-blue light, near the middle of the visible band, which is why sunlight appears white.
The peak wavelength tells you the dominant colour of an object's thermal glow. At 5772 K the Sun peaks around 502 nm in the green-blue, yet it emits across the whole visible range, so the mix reads as white. Cooler objects peak at longer wavelengths: a 3000 K incandescent filament peaks near 966 nm, in the near-infrared, which is why so much of its output is wasted heat rather than visible light. Hotter objects peak at shorter wavelengths — a 10,000 K star peaks in the ultraviolet and looks distinctly blue-white. Because the relationship is inverse, the colour shift is steep: raise the temperature and the peak marches left across the spectrum from red toward blue. That single number is how astronomers read a star's surface temperature straight from its colour, and how engineers reason about the glow of anything from a kiln to a tungsten lamp.
The formula is exact, but a couple of practical points are worth keeping in mind.
Ideal blackbody and absolute temperature
This calculator assumes an ideal blackbody and gives the wavelength of peak emission, not the only wavelength emitted — a real spectrum spreads on both sides of the peak. Surfaces with an emissivity below one emit slightly differently, though the inverse temperature relationship still holds well. Always use an absolute temperature in kelvin: convert from Celsius by adding 273.15, and remember the law is undefined at or below absolute zero.