Snell's Law Calculator
Calculate the angle of refraction as light passes between two media.
Assumptions used in this calculation
- Isotropic, homogeneous media: Assumes uniform refractive indices for each medium and a flat interface between them.
About this calculator
Light bends when it crosses from one transparent medium into another, air into water, or glass into air, which is why a straw looks broken in a glass of water, and predicting exactly how much it bends requires relating the two media's refractive indices to the incoming and outgoing angles. This calculator applies Snell's Law, n₁sin(θ₁) = n₂sin(θ₂), where n₁ and n₂ are the refractive indices of the first and second media and θ₁ is the angle of incidence, solving algebraically for θ₂, the angle of refraction. Enter both refractive indices and the incidence angle, and it returns the refraction angle directly, rearranging the equation and computing an inverse sine by hand is a step most people would rather skip. It also flags total internal reflection, which occurs when light traveling from a denser to a less dense medium hits the boundary beyond a critical angle, in that case no refraction angle exists because all the light reflects back, the principle behind fiber optic cables. This assumes uniform refractive indices and a flat interface between isotropic, homogeneous media.
Worked example
Light entering water from air at 30°
Result: 22.08°
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