Light bends when it changes speed between materials, which is why straws look broken in water.
How to use the Snell’s Law Calculator
- First medium
- Second medium
- Angle of incidence
Results update as you type, and every field accepts the units shown in its menu.
How it works
Multiply n₁ by the sine of the incident angle, divide by n₂ and take the arcsine.
Inputs explained
| Field | What to enter |
|---|---|
| First medium | Choose one: Air (1.0003), Water (1.333), Glass (1.52), Diamond (2.417) |
| Second medium | Choose one: Air (1.0003), Water (1.333), Glass (1.52), Diamond (2.417) |
| Angle of incidence | In ° |
Example values
How the main result changes when Angle of incidence changes and everything else stays at the example values above:
| Angle of incidence (°) | Angle of refraction (°) |
|---|---|
| 15 | 11.199 |
| 22.5 | 16.689 |
| 30 | 22.037 |
| 37.5 | 27.182 |
| 45 | 32.047 |
| 60 | 40.532 |
Formula
n₁ sin θ₁ = n₂ sin θ₂Critical angle = arcsin(n₂ ÷ n₁)Worked example
Inputs — First medium: Air (1.0003); Second medium: Water (1.333); Angle of incidence: 30 °.
Results — Angle of refraction = 22.037 °.
Frequently asked questions
Why is there no refraction angle sometimes?
Above the critical angle, light is totally internally reflected.
How do optical fibres work?
Total internal reflection keeps light inside the glass core.
What formula does the Snell’s Law Calculator use?
n₁ sin θ₁ = n₂ sin θ₂.