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Snell's Law Calculator.

Calculate a refracted angle using Snell's law.

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01

Set your values

Results update as you type.

Refracted angle: 19.471221 °

Refracted angle

0.000000°
Sine of refracted angle: 0.333333

Sine of refracted angle

0.000000

Results update automatically as you type.

Use Cases

Physics Homework and Study

Quickly verify refracted angles for optics problems involving light passing between different media, such as air to glass or water.

Example: Find the refracted angle when light enters glass (n=1.5) from air (n=1) at 30°.

Optical Design and Engineering

Use for preliminary calculations when designing lenses, prisms, or fiber optic systems where refraction angles are critical.

Example: Determine the bending of light in a glass prism with a given incident angle.

Frequently Asked Questions

What is Snell's law and how does this calculator use it?
Snell's law relates the angles of incidence and refraction to the refractive indices of two media. This calculator uses your inputs for incident refractive index, incident angle, and transmitted refractive index to compute the refracted angle.
What units are used for the incident angle?
The incident angle is entered in degrees (°). The calculator then computes the refracted angle in degrees as well.
Can I use this calculator for total internal reflection?
If the calculated refracted angle would exceed 90°, total internal reflection occurs. This calculator will indicate that no refraction is possible under those conditions.

Tips & Common Mistakes

Tips

  • Ensure the incident refractive index and transmitted refractive index are positive numbers. Typical values are 1.0 for air, about 1.33 for water, and about 1.5 for glass.
  • The incident angle must be between 0° and 90°. Angles outside this range are not physically meaningful for refraction at a boundary.
  • Double-check your units: the calculator expects the incident angle in degrees, not radians.

Common Mistakes to Avoid

  • Entering the incident angle in radians instead of degrees, which leads to incorrect results.
  • Using a negative value for refractive index, which is not physically possible.
  • Forgetting that total internal reflection occurs when the refracted angle would be greater than 90°, so the calculator may not return a valid angle.

Last updated: August 13, 2026