Beam Divergence Calculator

This is a beam calculator that we use to calculate divergence. Note that for a worst-case measurement, we calculate w₀ at 0. This is a more accurate measurement for close range calculations.

Calculate laser beam divergence using the measured beam radius and the distance from the laser output to the measurement point.

Initial Beam Radius, w₀ (mm)

w₀ is fixed at 0 mm for this calculation.

Beam Radius at Measurement Point, w (mm) Distance from Laser Output, L (m)

Full-Angle Beam Divergence

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Half-Angle Divergence: —

Full-Angle Divergence in Degrees: —

Beam Divergence Calculation

General equation:

θ_half = (w − w₀) / L

Since w₀ = 0:

θ_half = w / L

θ_full = 2w / L

w₀ = Initial beam radius at laser output (fixed at 0 mm)

w = Beam radius at measurement point (mm)

L = Distance from laser output to measurement point (m)

θ_half = Half-angle divergence (mrad)

θ_full = Full-angle divergence (mrad)

Koechner W. Solid-State Laser Engineering. 6th ed. New York, NY: Springer; 2006
Paschotta R. M² Factor. RP Photonics Encyclopedia. RP Photonics AG. Available at: https://www.rp-photonics.com/m2_factor.html [Accessed August 2026]