🔺 Laser Beam Divergence Calculator
Estimate how much a laser beam spreads out (divergence) based on its wavelength and beam waist, using the Gaussian beam approximation.
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What beam divergence is
Laser beam divergence is the rate at which a laser beam spreads out as it travels away from its source. It is an important property in optics, ranging, and laser safety applications.
The formula
For a Gaussian beam, the far-field divergence half-angle is θ = λ / (πw0), where λ is the wavelength and w0 is the beam waist radius. The beam radius at distance L is w(L) = w0√(1 + (λL / πw0²)²), which combines near-field and far-field behavior into one expression.
This is the standard idealized Gaussian beam model; real laser beams may diverge somewhat differently due to beam quality (M² factor) and optical imperfections.
Last reviewed August 2026