Diopter Calculator

What Is a Diopter?

A diopter (D) measures the optical power of a lens. It tells you how strongly a lens converges or diverges light. Eyeglass prescriptions, camera lenses, and magnifiers all use diopters or equivalent focal length values.

Diopter Formula

$$D = \frac{1}{f}$$

$D$ is lens power in diopters and $f$ is focal length in meters. A +2 D lens has focal length $f = 1/2 = 0.5\,\text{m} = 500\,\text{mm}$. Negative diopters indicate diverging (concave) lenses used for myopia correction.

Converting Focal Length Units

Always convert focal length to meters before applying the formula. One millimeter equals 0.001 m, and one centimeter equals 0.01 m. The calculator handles mm, cm, and m inputs automatically.

Frequently Asked Questions

What does a positive diopter value mean?

Positive diopters indicate a converging (convex) lens that brings parallel light to a focus. Reading glasses and magnifiers typically have positive power.

What does a negative diopter value mean?

Negative diopters indicate a diverging (concave) lens that spreads parallel light. Nearsighted prescriptions use negative lens power.

How do I convert 500 mm to diopters?

Convert to meters first: 500 mm = 0.5 m. Then D = 1/0.5 = +2 D.

Can I add diopters from two thin lenses?

Yes, for thin lenses in contact, total power is the sum of individual diopters: D_total = D₁ + D₂.

What happens at zero diopters?

Zero diopters means infinite focal length, equivalent to a flat pane of glass with no optical power.

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What Is a Diopter?

Diopter Formula

Converting Focal Length Units

Frequently Asked Questions

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