Snell's Law Calculator

What Is a Snell's Law (Refraction) Calculator?

Snell's Law describes how light bends when it passes from one transparent material into another — like from air into water or glass — because light travels at different speeds in different materials. This calculator finds the refraction angle from the two materials' refractive indices and the incoming angle.

How to Use This Snell's Law (Refraction) Calculator

1. Enter the refractive index of the first material (n1) — air is about 1.0.
2. Enter the incident angle θ1, measured from the normal (perpendicular) line, in degrees.
3. Enter the refractive index of the second material (n2) — water is about 1.33, glass about 1.5.
4. Click Calculate to get the refraction angle θ2.

Formula

• n1 × sin(θ1) = n2 × sin(θ2)

Worked Example

Light travels from air (n1 = 1.0) into water (n2 = 1.33) at a 40° incident angle. sin(θ2) = (1.0/1.33) × sin(40°) ≈ 0.483, so θ2 = arcsin(0.483) ≈ 28.9°.