Physics

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Mirror Equation Calculator.

Solve the paraxial mirror equation for image distance and magnification.

On-device calculationNo signup
01

Set your values

Results update as you type.

Image distance: 0.333333 m

Image distance

0.000000m
Magnification: -0.666667

Magnification

0.000000

Results update automatically as you type.

Use Cases

Physics homework and exam prep

Quickly verify your manual calculations for mirror problems, ensuring you understand the relationship between focal length, object distance, and image properties.

Example: Check a concave mirror with f = 0.2 m and object at 0.5 m.

Optics lab verification

Use the calculator to predict image distance and magnification before setting up an optical bench, saving time and reducing errors.

Example: Plan an experiment with a convex mirror of f = -0.15 m and object at 0.3 m.

Frequently Asked Questions

What does the Mirror Equation Calculator do?
It solves the paraxial mirror equation (1/f = 1/do + 1/di) for image distance and magnification. You input the focal length and object distance in meters, and it calculates the image distance and magnification for a spherical mirror.
What units should I use for focal length and object distance?
Both focal length and object distance must be entered in meters (m). The calculator will output the image distance in meters and magnification as a dimensionless number.
Can this calculator handle both concave and convex mirrors?
Yes, the sign convention is built in. Use a positive focal length for concave mirrors and a negative focal length for convex mirrors. The calculator will correctly determine the image distance and magnification.

Tips & Common Mistakes

Tips

  • Remember the sign convention: positive focal length for concave mirrors, negative for convex mirrors.
  • Ensure both inputs are in meters; convert from centimeters or millimeters if needed.
  • If the object is at the focal point (do = f), the image is at infinity; the calculator may show a very large value or an error.
  • Use the magnification to determine if the image is upright (positive) or inverted (negative).

Common Mistakes to Avoid

  • Forgetting to convert units to meters before entering values.
  • Using the wrong sign for the focal length (e.g., positive for convex mirrors).
  • Misinterpreting magnification: a negative magnification means an inverted image, not a smaller image.

Last updated: August 13, 2026