Law of Reflection Calculator

How it works

1. 1Enter the angle of incidence — the angle between the incoming ray and the normal (perpendicular to the surface).
2. 2The law of reflection states θᵣ = θᵢ, so the calculator returns that same angle as the angle of reflection.
3. 3Watch the live diagram show both the incident and reflected rays symmetric about the normal.

Use cases

• Optics and physics students verifying mirror reflection problems.
• Engineers designing periscopes, laser beam paths, and optical instruments.
• Architects and lighting designers calculating how light bounces off reflective surfaces.

Frequently asked questions

What is the law of reflection?

The angle of incidence equals the angle of reflection: θᵢ = θᵣ. Both are measured from the normal — the line perpendicular to the surface — not from the surface itself. A ray hitting a mirror at 30° from the normal reflects at exactly 30° on the other side.

Why are angles measured from the normal, not the surface?

Measuring from the normal gives a consistent reference for any surface orientation. From the surface you would get the complement (90° − θ). A ray 30° from the normal is 60° from the surface; the law θᵢ = θᵣ always uses the normal convention.

What is the difference between specular and diffuse reflection?

Specular reflection (smooth mirror) follows θᵢ = θᵣ exactly, giving a clear image. Diffuse reflection (rough surface) scatters light in many directions, though each microscopic facet still obeys θᵢ = θᵣ. Matte walls reflect diffusely; polished metal reflects specularly.