Calculate Wien peak wavelength, Stefan-Boltzmann power, Planck spectral radiance, and emission color for any temperature. Explore blackbody physics with star presets.
The **Blackbody Radiation Calculator** applies the three pillars of thermal radiation physics — Wien's displacement law, the Stefan-Boltzmann law, and Planck's spectral distribution — to any temperature. Enter the temperature of a star, furnace, light bulb, or even the human body, and the calculator returns the peak wavelength, total radiated power, spectral radiance at any requested wavelength, and an approximate emission colour.
Blackbody radiation is central to astrophysics (stellar classification), materials science (thermal processing), lighting design (colour temperature), and climate science (Earth's energy balance). A perfect blackbody with emissivity ε = 1 radiates the maximum possible power at every wavelength; real objects radiate less, scaled by their emissivity.
Use the presets for the Sun, Sirius A, Betelgeuse, an incandescent bulb, lava, the human body, or the cosmic microwave background. The spectrum table reveals how radiance distributes from UV through visible to infrared, and the temperature table shows how peak wavelength and total power scale.
Use this calculator when you want the main thermal-radiation relationships in one place instead of juggling separate Wien, Stefan-Boltzmann, and Planck calculations.
It is useful for star temperatures, furnace radiation, infrared intuition, emissivity checks, and any situation where temperature needs to be tied to both spectrum shape and total radiated power.
Wien's Law: λ_peak = 2.898×10⁻³ / T [m] Stefan-Boltzmann: P = εσAT⁴ [W] Planck's Law: B(λ,T) = 2hc² / (λ⁵ (e^(hc/λkT) − 1)) where σ = 5.670×10⁻⁸ W/m²K⁴, h = 6.626×10⁻³⁴ J·s, c = 3×10⁸ m/s, k = 1.381×10⁻²³ J/K.
Result: Peak at 501 nm (green-yellow), 63.2 MW/m² total power
The Sun's surface at 5 778 K peaks at about 501 nm — smack in the middle of the visible spectrum. Total power per square metre is about 63 MW.
Blackbody physics is easiest to interpret when you separate three questions: where the spectrum peaks, how much total power is emitted, and what the spectrum looks like away from the peak. Wien's law answers the first, Stefan-Boltzmann the second, and Planck's law the third.
The most common mistake is treating a real object as an ideal blackbody without checking emissivity. Another is overinterpreting the peak colour: a hot source can peak in one part of the spectrum while still emitting broadly across many wavelengths. For real lamps, LEDs, and surfaces, blackbody behavior is often a useful reference rather than a perfect model.
An idealised object that absorbs all incident radiation and re-emits it thermally. Its spectrum depends only on temperature.
The peak is near green, but the broad spectrum covers all visible wavelengths, producing white light. Atmosphere scattering adds the yellow tinge.
The ratio of actual radiation to blackbody radiation at the same temperature. Polished metals have low ε (~0.05); oxides and organics are near 1.
The cosmic microwave background is a near-perfect blackbody at 2.725 K, peaking in the microwave range at about 1 mm wavelength.
Stefan-Boltzmann power goes as T⁴. Doubling temperature increases radiated power 16-fold.
LEDs and fluorescents are not blackbodies. Their "colour temperature" is the temperature of a blackbody that appears a similar colour, but the spectrum is very different.