About the Refractive Index Calculator
Refractive index from the speed of light in a medium, or from angles of incidence and refraction.
Also known as: index of refraction, n = c/v, optical density.
How to use this calculator
- Enter calculate from and the other fields.
- The result updates instantly as you type — press Calculate (or Enter) at any time.
- Review the breakdown shown under the main result.
- Use Copy result or Share to save the answer or send a link with your inputs.
Formula
n = c / v · n₁sin θ₁ = n₂sin θ₂
Worked example
Using the values pre-filled in the calculator above:
- Calculate from: Speed of light in the medium
- Speed in medium = 200,000,000 m/s
the calculator returns:
- Refractive index: 1.49896
- Speed of light in medium: 200,000,000 m/s
- Critical angle (to air): 41.846°
- Closest material: Glass