The vacuum speed of light is fixed at 299,792,458 m/s. Choose the refractive index or phase speed to solve, then enter the other value. The index of refraction is calculated with the formula presented below (n = c / v), which is the definition of refractive index in terms of wave speed. This calculator can also use Snell’s Law for positive real indices at an interface: n₁ sin(θ₁) = n₂ sin(θ₂). Measure angles from the normal, from 0° to 90°. Above the critical angle, the transmitted-ray solve reports total internal reflection.

Uses positive real phase indices for transparent, isotropic media. Angles are measured from the normal, from 0° to 90°. Vacuum light speed c = 299,792,458 m/s exactly; refractive index depends on wavelength.

Index of Refraction Formula

The formula for calculating a refractive index from wave speed is as follows:

n = c / v
  • Where n is the index of refraction
  • c is the speed of light in a vacuum = 299,792.458 km/s (299,792,458 m/s)
  • v is the speed of light in a given medium

To calculate an index of refraction, divide the speed of light in a vacuum by the speed of light in the medium.

Index of Refraction Definition

An index of refraction is the ratio of the speed of light through a vacuum with respect to the speed of light through some other medium, such as water.

How to calculate index of refraction?

How to calculate index of refraction?

  1. First, determine the speed of light in a vacuum.

    The speed of light in a vacuum is known to be 299,792.458 km/s (299,792,458 m/s).

  2. Next, measure the speed of light in the medium.

    For example, the speed of light through water is about 225,000 km/s (for n ≈ 1.33).

  3. Finally, calculate the index of refraction.

    Using the formula above and values from steps 1 and 2, calculate the index of refraction.

FAQ

What is an index of refraction?

An index of refraction is the ratio of the speed of light through a vacuum with respect to the speed of light through some other medium, such as water.