A blackbody radiation calculator applies two fundamental physics laws: Wien's Displacement Law (peak emission wavelength) and the Stefan-Boltzmann Law (total radiated power). Any object above absolute zero emits thermal radiation — hotter objects emit more intensely and at shorter wavelengths.
Blackbody Radiation
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How to Use the Blackbody Radiation Calculator
Blackbody radiation describes how all objects emit electromagnetic radiation based on their temperature. This calculator handles two key equations used in astrophysics, thermal engineering, and spectroscopy.
Step 1: Choose Your Calculation Mode
Select "Wien's Law" to find the peak wavelength of emitted radiation, or "Stefan-Boltzmann" to calculate total radiated power. Wien's Law is useful for identifying what part of the spectrum an object emits most strongly; Stefan-Boltzmann gives the total energy output.
Step 2: Enter Temperature
Choose your temperature unit (Kelvin, Celsius, or Fahrenheit). Enter the object's temperature. Note: the Stefan-Boltzmann law requires temperature in Kelvin, so all values are converted internally.
Step 3: Stefan-Boltzmann Inputs
For power calculations, also enter emissivity (ε) between 0 and 1 (1 = perfect blackbody, most real objects are 0.90–0.98) and surface area in square meters.
Example: The Sun
The Sun's surface temperature is ~5778 K. Wien's Law gives: λ_max = 2.898×10⁻³ / 5778 = 501.6 nm (green visible light). The Stefan-Boltzmann law gives ~6.3×10⁷ W/m² at the surface with ε ≈ 1.
FAQ
What is Wien's Displacement Law?
Wien's Displacement Law states that the peak wavelength of blackbody radiation is inversely proportional to temperature: λ_max = 2.898×10⁻³ m·K / T. Hotter objects emit at shorter (bluer) wavelengths; cooler objects emit at longer (redder) wavelengths.
What is the Stefan-Boltzmann Law?
The Stefan-Boltzmann Law gives total power radiated per unit area: P = εσT⁴, where ε is emissivity (0-1), σ = 5.67×10⁻⁸ W/(m²K⁴), and T is temperature in Kelvin. A perfect blackbody has ε = 1.
What temperature is the Sun's surface?
The Sun's surface temperature is about 5778 K, which gives a peak wavelength of about 502 nm — right in the green part of the visible spectrum. However, our atmosphere and eye sensitivity make the sun appear yellow-white.
Is this calculator free?
Yes, completely free with no signup required. All calculations happen in your browser.
What is emissivity?
Emissivity is a dimensionless number from 0 to 1 that describes how efficiently a surface radiates heat compared to a perfect blackbody. Most real materials have emissivity between 0.9 and 0.98. A perfect blackbody has ε = 1.