Lighting Tool
Beam Angle & Throw Distance Calculator
Calculate beam diameter and coverage area from throw distance and beam angle, or find the minimum beam angle needed to hit a target diameter.
Calculate beam spread and throw distance
Enter a throw distance and beam angle to get beam diameter and coverage area — or work in reverse to find the minimum angle needed for a target spot size.
How to use the beam angle calculator
- Choose Forward mode to calculate beam diameter from throw distance and angle.
- Choose Reverse mode to find the required beam angle for a target diameter.
- Toggle between full-angle and half-angle if your fixture spec uses field angle.
- Switch between metres and feet as needed.
Notes
Full angle vs half-angle
Manufacturers list beam angle as either the full cone (tip to tip) or the half-angle (centre to edge). Toggle the type to match your fixture spec.
Throw distance
Measured from the front lens to the lit surface. Longer throws need narrower angles for tight spots.
Coverage area
Assumes a circular beam footprint. Angled throws produce elliptical spots — add a correction factor for steep angles.
Reverse mode
Useful when you know the surface size and distance and need to select the right fixture or attachment.