About the Lens Power Calculator
Lens power in diopters from focal length (and back), plus the combined power of two lenses.
Also known as: diopter calculator, glasses prescription power, optical power.
How to use this calculator
- Enter calculate, second lens power (optional).
- The result updates instantly as you type — press Calculate (or Enter) at any time.
- Review the breakdown shown under the main result.
- Use Copy result or Share to save the answer or send a link with your inputs.
Formula
P (diopters) = 1 / f (metres)
Worked example
Using the values pre-filled in the calculator above:
- Calculate: Power from focal length
- Focal length = 50 cm
- Second lens power (optional) = 0 D
the calculator returns:
- Lens power: 2 D
- Lens type: Converging (+)