Enter the real distance (ft) and the refractive index into the Calculator. The calculator will evaluate the Apparent Distance. 

Apparent Distance Formula

AD = RD / RI


  • AD is the Apparent Distance (ft)
  • RD is the real distance (ft)
  • RI is the refractive index

To calculate the Apparent Distance, divide the real distance by the refractive index.

How to Calculate Apparent Distance?

The following steps outline how to calculate the Apparent Distance.

  1. First, determine the real distance (ft). 
  2. Next, determine the refractive index. 
  3. Next, gather the formula from above = AD = RD / RI.
  4. Finally, calculate the Apparent Distance.
  5. After inserting the variables and calculating the result, check your answer with the calculator above.

Example Problem : 

Use the following variables as an example problem to test your knowledge.

real distance (ft) = 4

refractive index = 1.234


What is the refractive index?

The refractive index, often symbolized as RI or n, is a dimensionless number that describes how light, or any other radiation, propagates through that medium. It is defined as the ratio of the speed of light in a vacuum to the speed of light in the medium.

Why is apparent distance different from real distance?

Apparent distance differs from real distance due to the phenomenon of refraction. When light passes from one medium into another, its speed changes, causing it to bend or refract. This bending of light makes objects appear closer or farther away than they actually are, thus altering their apparent distance.

How does temperature affect the refractive index?

Temperature can significantly affect the refractive index of a medium. Generally, as the temperature increases, the refractive index decreases. This is because the density of the medium changes with temperature, which in turn affects how light propagates through it.

Can the apparent distance formula be used for any type of wave?

While the formula provided primarily applies to light waves, the concept of apparent distance can be extended to other types of waves, such as sound waves, under certain conditions. However, the specific factors influencing apparent distance might differ, such as the medium’s properties and the wave’s frequency.