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Refractive Index Calculator

Work out refractive index instantly with clear inputs, formula shown and shareable results.

About Refractive Index Calculator

Refractive index is the ratio of the vacuum speed of light to its speed in the medium, n = c/v. Light at 2.0e8 m/s gives n = 1.499, typical of crown glass. Frequency is unchanged on entering the medium, so the wavelength shortens by the same factor - 589 nm sodium light becomes 393 nm inside the glass.

Formulas

Refractive index

n = c / v

Wavelength inside

lambda(medium) = lambda(vacuum) / n

Worked example

With the default values below, Refractive Index Calculator returns Refractive Index of 1.4990. Change any input above and every figure here is recalculated in your browser.

Inputs used

Speed of light in the mediumminimum 0 m/s
200,000,000 m/s
Wavelength in vacuumminimum 0 nm
589 nm

Results

Refractive Index
1.4990
Wavelength Inside The Medium
392.939 nm
Critical Angle At An Air Boundary
41.846 deg
How Much Light Is Slowed
33.29%

Step by step

  1. 1Values used
  2. 2Refractive index
  3. 3Wavelength inside
  4. 4Refractive Index= 1.4990
  5. 5Wavelength Inside The Medium= 392.939 nm
  6. 6Critical Angle At An Air Boundary= 41.846 deg
  7. 7How Much Light Is Slowed= 33.29

Assumptions and limits

  • The result is derived only from the 2 inputs listed above. Anything not among them is not part of the calculation.
  • In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
  • Figures are rounded for display to 4 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Frequently Asked Questions

Does the colour change inside glass?

No. Colour follows frequency, which does not change. Only the wavelength contracts, which is why the light looks the same on emerging.

Can the refractive index be below one?

The phase index can be, in plasmas and near absorption lines, but the group velocity carrying information never exceeds c.

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