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Refraction Index Calculator – Calculate Refractive Index

Calculate the refractive index of a material from the speed of light or wavelength ratio. Our calculator helps determine optical properties.

How to Use This Refraction Index Calculator

1

Choose calculation method

Select whether to calculate from speed of light or wavelength ratio.

2

Enter your values

Input the speed of light in the material or the wavelengths in vacuum and material.

3

Get the refractive index

The calculator computes the refractive index (n) instantly.

Understanding Refractive Index

The refractive index (n) measures how much light slows down when passing through a material. It is the ratio of the speed of light in vacuum to the speed in the material.

n = c / v
n = λ₁ / λ₂

Higher refractive index means light travels slower and bends more. Vacuum has n = 1. All other materials have n > 1.

Refractive Index of Common Materials

MaterialRefractive Index (n)Light Speed
Vacuum1.000299,792 km/s
Air (STP)1.0003299,702 km/s
Water (20°C)1.333225,000 km/s
Crown Glass1.52197,000 km/s
Diamond2.42124,000 km/s
Silicon3.9675,700 km/s

Snell's Law and Refraction

When light passes from one material to another, it bends. Snell's Law describes this bending:

n₁ × sin(θ₁) = n₂ × sin(θ₂)

Where θ₁ is the incident angle and θ₂ is the refracted angle. Light bends toward the normal when entering a denser material (higher n).

Frequently Asked Questions

What does refractive index tell us?
Refractive index shows how much light slows down in a material. It also determines how much light bends at the interface. Higher n means slower speed and more bending.
Can refractive index be less than 1?
Not for normal materials. Vacuum has n = 1, and all materials have n > 1. Metamaterials can have negative refractive index, but this is a special case.
Why does diamond sparkle?
Diamond has a high refractive index (2.42), causing significant light bending. Combined with its dispersion (splitting white light into colors), this creates the characteristic sparkle and fire.
Does refractive index change with color?
Yes. This is called dispersion. Blue light typically has a slightly higher refractive index than red light, which is why prisms split white light into a rainbow.
What is critical angle?
When light goes from high-n to low-n material, there is an angle where all light reflects back. This is total internal reflection, used in fiber optics.

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