Index of refraction illustration with a light beam traveling from a vacuum into a medium material.
absolute index of refraction
Speed in medium (v)
Index of refraction
To calcualate the angle of refraction, use our Snell's law calculator 🐌

Index of Refraction Calculator

By Bogna Szyk and Steven Wooding
Last updated: Aug 12, 2020

The index of refraction calculator will allow you to calculate the refractive index of any medium. It is also a tool useful for determining the speed of light in any medium. Continue reading to discover the index of refraction formula and learn how to find the index of refraction.

Refractive index definition

The index of refraction, also called the refractive index, describes how light propagates through a medium. It is a dimensionless quantity, and it determines how much light is bent (refracted) when entering a different medium. In essence, refraction means a change in the speed and wavelength of the wave.

Index of refraction formula

Index of refraction of any medium is defined as the proportion between the light of speed in vacuum and in the investigated medium. The refractive index equation is:

n = c / v


  • c is the speed of light in vacuum - 299,792.46 km/s,
  • v is the speed of light in the medium, and
  • n is the refractive index.

The typical values for the refractive index are between 1 and 2, but there are some higher values. As nothing can travel faster than with the speed of light, there are no materials with the index of refraction lower than 1.

How to find the index of refraction

  1. Determine the speed of light in the analyzed medium. For example, let's assume 228,850 km/s.
  2. Divide the speed of light by this value. 299792.46 / 228850 = 1.31.
  3. The obtained value is the refractive index of the medium.
  4. You can use this value to calculate the angle of refraction, using our Snell's law calculator.

You can also take the value of the refractive index directly from the list below.

  • Vacuum: 1 (by definition)
  • Air: 1.000293
  • Water at 20 °C: 1.333
  • Ethanol: 1.36
  • Ice: 1.31
  • Diamond: 2.419
Bogna Szyk and Steven Wooding