Blackbody Radiation Calculator

Enter temperature to get peak wavelength (Wien’s law) and radiated power (Stefan–Boltzmann). Optional emissivity and area compute total power. Private by design — everything runs locally in your browser.

Inputs

Temperature

Emissivity ε (0–1, default 1)

Area A (m²) (optional)

Output wavelength unit

Presets:

Results

Peak wavelength (Wien):

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Radiated power (Stefan–Boltzmann):

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q = ε σ T⁴ (W/m²); σ = 5.670374419×10⁻⁸ W·m⁻²·K⁻⁴

Total power (if A > 0):

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P = q · A

How This Blackbody Calculator Works

A perfect blackbody emits thermal radiation with a spectrum determined only by its absolute temperature T. Two cornerstone relations summarize the behavior. Wien’s displacement law gives the peak wavelength λ_max = b/T, with b ≈ 2.897771955×10⁻³ m·K. As temperature rises, the peak shifts to shorter wavelengths (toward blue/UV). Stefan–Boltzmann’s law gives the radiated power per unit area, q = ε σ T⁴, where σ = 5.670374419×10⁻⁸ W·m⁻²·K⁻⁴ and ε is emissivity (1 for a perfect blackbody). If you specify an emitting area A, the total power is P = qA.

The optional spectrum plot uses Planck’s law in wavelength form, B_λ(λ,T) = (2hc²/λ⁵) / (e^{hc/(λkT)} − 1), normalized to a peak of 1 for clarity. This visualization helps connect temperature to color: room-temperature objects peak in the infrared, the Sun peaks in visible green-yellow (~500 nm), and very hot objects peak in the ultraviolet.

Tips: Temperature must be on an absolute scale (K). If you enter °C, we convert to K internally via T(K)=T(°C)+273.15. Emissivity ε ranges from 0–1; many real surfaces are 0.8–0.98. Outputs are SI: nm/µm/m for wavelength, W/m² for flux, and W for power.