Laser Beam Divergence Calculator

Find a laser's divergence angle from beam growth over distance.

Initial beam diameter

Beam diameter at distance

Distance

Full-angle divergence (mrad) 0.18

Formula: θ = (d₂ − d₁) ÷ distance

Step-by-step with your numbers:

1. Values used:

2. Initial beam diameter = 2

3. Beam diameter at distance = 20

4. Distance = 100

6. Full-angle divergence = 0.18mrad

Did we solve your problem today?

Even laser beams spread out a little; divergence measures how fast.

The math behind it

Full-angle divergence θ ≈ (d₂ − d₁) ÷ distance, expressed here in milliradians.

2 mm to 20 mm over 100 m → 0.18 mrad.

Why does it spread at all?

Diffraction limits how parallel any real beam can be.