Malus's Law Calculator

Your details

Choose which quantity to compute. The other two become inputs.
The irradiance of the incident (incoming) polarized light, in watts per square metre.
W/m²
The angle between the transmission axis of the polarizer and the polarization direction of the incident light, in degrees (0° to 90°).
°
When enabled, a first ideal polarizer halves the intensity before Malus's law is applied (unpolarized light: I₀/2 enters the analyzer).
Transmitted intensity (I)Moderate transmission
50W/m²

Irradiance after the polarizer

Intensity ratio (I / I₀)0.5
Transmission50%
50 %
Near-blocked<10High attenuation10-50Moderate50-90Near-full90+

50.00% of the polarized intensity is transmitted.

  • At θ = 45°, cos²(θ) = 0.5000, so 50.00% of the input intensity passes through.
  • At 45° the polarizer passes exactly half of the incoming polarized intensity (cos² 45° = 0.5).
  • Transmitted intensity: 50.0000 W/m².
  • Malus’s law applies only to linearly polarized light. Real polarizers also absorb some in-axis light, so measured transmission is typically a few percent below cos²(θ).

Next stepTo stack two polarizers, apply Malus’s law twice: first at the angle between source and polarizer 1, then at the angle between polarizer 1 and polarizer 2.

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