🔺 Critical Angle Calculator
Calculate the critical angle for total internal reflection between two optical media.
Total Internal Reflection
When light travels from a denser (higher-index) medium into a less dense one, there’s a specific angle of incidence — the critical angle — beyond which the light no longer refracts out but instead totally internally reflects. It’s found from Snell’s law at the point where the refraction angle reaches 90°: θc = arcsin(n2/n1).
This effect is essential for fiber optics, prisms, and underwater visibility. If n2 is greater than or equal to n1, no critical angle exists because light is always moving into a denser or equal medium.
Last reviewed August 2026