Snell's Law Calculator
Compute light refraction at an interface with Snell's law n₁·sinθ₁ = n₂·sinθ₂. Find the refraction angle from the incidence angle and two refractive indices (with a small material-index library: air, water, ice, acrylic, crown glass, flint glass, sapphire, diamond), or the critical angle for total internal reflection. The calculator flags total internal reflection when the angle exceeds the critical angle (light cannot refract and reflects internally). Pairs with the Thin Lens Equation and Depth of Field calculators for optics work. Everything runs locally in your browser.
Snell's law n₁·sinθ₁ = n₂·sinθ₂ governs the bending of light at the interface between two transparent media (angles measured from the normal). Light entering a denser medium (higher n) bends toward the normal; entering a rarer medium it bends away. When going from dense to rare at an angle steeper than the critical angle θ_c = arcsin(n₂/n₁) (requires n₁ > n₂), no light refracts and total internal reflection occurs. To find an unknown index, rearrange: n₂ = n₁·sinθ₁ / sinθ₂. Everything runs locally — nothing leaves your browser.