basic

Lensmaker's Equation Focal Length Calculator

1 / f = (n − 1) · (1 / R₁ − 1 / R₂) for a thin lens.

Compute the focal length of a thin lens from the refractive index of the lens material and the radii of curvature of the two faces, using the lensmaker's equation: 1 / f = (n − 1)(1 / R₁ − 1 / R₂). Reports the focal length and lens power in dioptres.

Dr. Helena Ortiz By Dr. Helena Ortiz
Published Last reviewed 1 min read

Inputs

cm
cm

Results

Enter values and click Calculate to see results.
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How to use this calculator

  1. Fill in the inputs above using the units you already have.
  2. Values update automatically as you type — no submit button needed.
  3. Hover any result row for the underlying formula and intermediate values.

Formula

1 / f = (n − 1) · (1 / R₁ − 1 / R₂); D = 1 / f (m).

In depth

Compute the focal length of a thin lens from the refractive index of the lens material and the radii of curvature of the two faces, using the lensmaker's equation: 1 / f = (n − 1)(1 / R₁ − 1 / R₂). Reports the focal length and lens power in dioptres.