Malus Law Calculator

Written by Great Medico

Updated September 25, 2026 •2 min read

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The value of a malus law calculator is speed without losing the physics behind the answer. Optical formulas are compact, but their sign conventions and geometric assumptions deserve as much attention as the arithmetic. Keep that relationship in view as you replace the defaults with your own data.

What this calculator does

This page focuses on transmitted intensity from Initial intensity, Angle of incidence. The calculation stays deliberately narrow: it uses the fields tied to this relationship and reports related quantities only when they follow from those same inputs.

How to use it

Enter Initial intensity, Angle of incidence from the same physical setup, keeping every unit consistent with the selector shown on the page. After the result appears, make one small input change as a sanity check rather than relying on the first number simply because it has several decimal places.

How the calculation works

Malus’ law is applied as I = I₀cos²θ, where I₀ is the incident polarized intensity and θ is the relative polarization angle. The page also reports transmission as 100·I/I₀ percent.

Example

Using the default example on the page (Initial intensity = 1 W/m²; Angle of incidence = 45 deg), the calculator returns transmitted intensity of 0.5 W/m². This baseline lets you confirm the calculation path before entering a different geometry, material, speed, or operating condition.

How to interpret the result

Use the transmitted intensity for comparisons made under the same optical assumptions. The displayed unit matters, and so does whether the page is describing power, intensity, focal geometry, angular field, or transmission—quantities that should not be treated as interchangeable.

Limitations and notes

Real optical systems can add aberration, alignment error, finite bandwidth, diffraction, scattering, detector response, and component tolerances beyond the ideal relationship shown here. Pay particular attention to Initial intensity, Angle of incidence. If the real system includes effects that are not represented on the form, the calculated number can be internally correct yet incomplete for design. Use governing standards and test data where consequences matter.