Mirror Equation Calculator

Mirror Equation Calculator

Use the spherical mirror equation to solve for focal length, object distance, or image distance.

Last updated: June 2026 | By Patchworkr Team

Mirror sign-convention helper
The equation is 1/f = 1/do + 1/di. Sign conventions still matter, so positive and negative values are meaningful.
Result
Enter values to calculate

What the formula means

The mirror equation links three quantities for spherical mirrors. If the denominator becomes zero, the corresponding value is not finite.

Sign convention note

Concave mirrors are commonly treated with positive focal length, while convex mirrors are negative. Real and virtual images follow the same convention used in optics texts.

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