Apparent Depth (Refraction) Calculator

About this calculator

When light travels from one medium into another with a different refractive index — such as from water into air — it bends at the boundary, which is why a pool or pond always looks shallower than it actually is when viewed from above. For viewing close to straight down, this can be approximated as apparent depth = real depth × (n2 ÷ n1), where n1 is the refractive index of the medium the object is in (water, ~1.33) and n2 is the medium the observer is in (air, ~1.0), so water's higher index compresses the perceived depth to about 75% of the real value.

This calculator takes the real depth and the two refractive indices and returns the apparent depth an observer would perceive. Physics students studying Snell's law and refraction, divers and spearfishers judging distances underwater, and photographers correcting for the visual distortion of shooting through water use it to understand or predict this everyday optical illusion.