Wien's Law Calculator: Peak Blackbody Wavelength

What this calculator does

Wien's law, also called Wien's displacement law, gives the wavelength at which a blackbody radiates most strongly at a given temperature: λmax = b/T, where b is Wien's displacement constant (2.897771955×10⁻³ m·K) and T is the object's absolute temperature in kelvin. As an object gets hotter its peak emission shifts to shorter wavelengths, which is why a heated metal glows red, then orange, then white as its temperature climbs.

The relationship is a simple inverse proportion: double the absolute temperature and the peak wavelength halves. This calculator takes a temperature and returns the peak wavelength in nanometres, micrometres and metres together, since the useful scale depends entirely on what kind of object is being considered, from a room-temperature surface radiating in the infrared to a hot star radiating in visible light.

The formula

Formulaλmax = b/T, b = 2.897771955×10⁻³ m·K

Divide Wien's displacement constant b = 2.897771955×10⁻³ m·K by the absolute temperature T, in kelvin: λmax = b/T. The result comes out in metres and is also shown converted to micrometres and nanometres, the more convenient scale for most peak wavelengths encountered in practice.

Term	Meaning
λmax	Peak wavelength: the wavelength at which the blackbody's emission is strongest.
b	Wien's displacement constant, 2.897771955×10⁻³ m·K.
T	Absolute temperature, in kelvin. Convert from Celsius by adding 273.15.

The inputs explained

Field	What to enter
Temperature (K)	The absolute temperature of the blackbody, in kelvin. To convert from Celsius, add 273.15; the sun's surface is about 5,778 K.

When to use it

Estimating a star's colour from its surface temperature

A star's spectrum peaks close to where Wien's law predicts for its surface temperature, which is why hotter stars look bluer and cooler stars look redder, even though every star radiates across a broad spread of wavelengths.

Working out roughly how hot something is from its colour

Run the other way, a peak wavelength observed in a spectrum can be used to back out the temperature by rearranging the formula to T = b/λmax, a common step in astrophysics and remote temperature sensing.

Understanding thermal imaging and infrared sensing

Objects near room temperature peak in the infrared, well outside visible light, which is exactly why thermal cameras are built to detect infrared wavelengths rather than visible ones to "see" heat.

Worked examples

Every figure in the tables below is produced by this page’s own calculator at build time, so the numbers and the tool always agree. Select any row to load that scenario.

How peak wavelength changes with temperature

A range of temperatures spanning everyday, industrial and astrophysical scales.

From body temperature to a hot star

Temperature	Peak wavelength (nm)	Peak wavelength (µm)
288 K	10,061.70818 nm	10.06170818 µm
310.15 K	9,343.130598 nm	9.3431306 µm
3000 K	965.923985 nm	0.96592399 µm
5778 K	501.5181646 nm	0.50151816 µm
6000 K	482.9619925 nm	0.48296199 µm
10000 K	289.7771955 nm	0.2897772 µm

At 288 K, close to average outdoor air temperature, the peak sits at 10,061.708 nm (10.062 µm), well into the infrared and invisible to the eye. At 5,778 K, the sun's surface temperature, the peak falls at 501.518 nm, in the visible green-blue part of the spectrum, close to where human vision is most sensitive.

Peak wavelength for some familiar and reference temperatures

Body temperature, a candle flame, an incandescent filament, the sun and a hot blue star, compared on the same scale.

From human body temperature to a hot blue star

Temperature	Peak wavelength (nm)
Human body (37°C)	9,347.651468 nm
Candle flame	1,525.143134 nm
Incandescent filament	1,034.918555 nm
Sun's surface	501.5181646 nm
Hot blue star	241.4809963 nm

Human body temperature peaks at 9,347.651 nm, deep infrared, which is why body heat is invisible without a thermal camera. A candle flame at 1,900 K peaks at 1,525.143 nm, still infrared; an incandescent filament at 2,800 K peaks at 1,034.919 nm, close enough to visible red that a filament bulb glows warm white; a 12,000 K blue star peaks at 241.481 nm, in the ultraviolet, past the blue end of what the eye can see directly.

Questions

What is Wien's law formula?

λmax = b/T, where b is Wien's displacement constant, 2.897771955×10⁻³ m·K, and T is the absolute temperature in kelvin. The peak wavelength and temperature are inversely proportional: doubling T halves λmax.

Do I need to enter temperature in Celsius or Kelvin?

Kelvin, since the formula requires absolute temperature. Convert from Celsius by adding 273.15: a temperature of 25°C is 298.15 K.

Does every object glow at its Wien's law peak wavelength?

Every object above absolute zero radiates across a broad range of wavelengths, not just the single peak. Wien's law only identifies where that spread is strongest; the shape of the full spectrum around that peak is described by the Planck blackbody radiation curve.

How does this relate to the Stefan-Boltzmann law?

Wien's law finds where a blackbody's emission peaks; the Stefan-Boltzmann law finds the total power it radiates across all wavelengths combined. Both depend only on temperature, but they answer different questions about the same emission spectrum.

For the total radiated power at a given temperature rather than the peak wavelength, see the Stefan-Boltzmann law calculator. For working with the photon energy at a specific wavelength once you have it, see the photon energy calculator.

Wien's displacement law calculator