Diopter Calculator
Convert focal length to diopters or back with P = 1/f, or add the powers of lenses placed together. Focal length is shown in meters and centimeters.
How to use the diopter calculator
- To convert, enter either a focal length in meters or a power in diopters.
- To combine lenses, enter the individual powers and they are summed.
- Read the optical power and the focal length in meters and centimeters.
Examples
Focal length to power
focal length = 0.5 m
power = 2 D
Power to focal length
power = 2 D
focal length = 0.5 m (50 cm)
Combine two lenses
powers = 2 D and 3 D placed together
total power = 5 D, focal length = 0.2 m
Frequently asked questions
What is a diopter?
A diopter is a unit of optical power equal to the reciprocal of the focal length in meters. A 0.5 m focal length lens has a power of 2 diopters.
How do I convert focal length to diopters?
Use P = 1 / f, with the focal length f in meters. A 0.25 m lens has a power of 4 diopters; a 2 m lens has 0.5 diopters.
How do I add lens powers?
For thin lenses placed close together, total power is the sum of the individual powers. Enter each power and the calculator adds them.
What does a negative diopter mean?
Negative power means a diverging lens with a negative focal length, used to correct nearsightedness. Positive power is a converging lens.
Why can the power or focal length not be zero?
Power is the reciprocal of focal length, so a focal length of zero is undefined and a power of zero would mean an infinite focal length.
Related tools
Lens Maker's Equation Calculator
Find a lens focal length and power from its refractive index and surface radii using 1/f = (n-1)(1/R1 - 1/R2). Supports flat surfaces. Free and instant.
Thin Lens Calculator
Solve the thin lens equation 1/f = 1/do + 1/di. Enter any two of focal length, object distance and image distance to find the third, plus magnification.
Lens Magnification Calculator
Solve the thin lens equation 1/f = 1/do + 1/di and find magnification m = -di/do. Enter any two of focal length, object and image distance. Free tool.
555 Timer Calculator
Calculate 555 timer astable frequency, period, high and low times and duty cycle from R1, R2 and the timing capacitor. Free oscillator design helper.
Absolute Humidity Calculator
Calculate absolute humidity in grams of water vapor per cubic meter from air temperature and relative humidity. Fast, free and works in your browser.
Allele Frequency Calculator
Find allele frequencies from genotype counts. Enter the number of AA, Aa and aa individuals to get the A and a allele frequencies and allele totals.