What is the Blackbody Radiation Calculator?
Calculate blackbody peak wavelength, Stefan–Boltzmann radiant exitance, and Planck spectral radiance with this free blackbody radiation calculator. Uses Wien's displacement law and σT⁴. Presets for the Sun, cosmic microwave background, and human body temperature. Runs entirely in your browser with no signup.
How to use the Blackbody Radiation Calculator
- Choose Bulk Properties, Planck Law (λ), or Planck Law (ν) mode.
- Enter temperature in kelvin.
- For Planck modes, also enter wavelength or frequency.
- Click Calculate to get peak wavelength, total flux, and spectral radiance.
- Copy results and step-by-step physics formulas.
Common use cases
- Finding the Sun's peak emission wavelength at 5778 K
- Calculating total thermal radiation from a surface at 310 K
- Computing Planck spectral radiance at 500 nm for stellar spectroscopy
Frequently asked questions
- What is Wien's displacement law?
- λ_max = b/T, where b ≈ 2.898 × 10⁻³ m·K. Hotter blackbodies peak at shorter wavelengths — the Sun at 5778 K peaks near 502 nm in the visible green.
- What is the Stefan–Boltzmann law?
- Total radiant exitance M = σT⁴, where σ ≈ 5.670 × 10⁻⁸ W/(m²·K⁴). It gives the total power radiated per unit area from a perfect blackbody.
- What is Planck's law?
- Planck's law gives spectral radiance B_λ or B_ν as a function of temperature and wavelength or frequency, accounting for quantum statistics of photons.
- What temperature is the cosmic microwave background?
- The CMB has a blackbody temperature of about 2.725 K, peaking near 1.06 mm wavelength (about 280 GHz).
