Enter the values exactly as they appear on your spectacle prescription. The calculator shows what a contact lens specification would say, what changes on the way and which lenses are made in those values.
Spectacle prescriptionYour entry
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Contact lens valuesGuide values
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Tap a column heading to see what the value means.
These are guide values only. Contact lenses are medical devices: base curve (BC) and diameter (DIA) can only be determined at a fitting by an optometrist or contact lens optician, and UK retailers may only supply lenses against a valid contact lens specification.
How the values are derived
Enter at least the sphere of one eye.
Lenses made in these values
Once the sphere of one eye is entered, matching lenses appear here.
Not included: 166 lenses without parameter data in the catalogue.
Why glasses values and contact lens values differ
If you want to try contact lenses, chances are all you have is your glasses prescription. Its values are a good starting point, but they cannot be copied one to one. Four things separate a spectacle lens from a contact lens.
Vertex distance
A spectacle lens sits about 12 millimetres in front of the eye, a contact lens sits on it. That distance changes the effect of a given power. Up to about ±4 dioptres the difference is smaller than a quarter step and disappears in rounding. Above that it shows: short-sighted wearers need slightly less minus in a lens, long-sighted wearers slightly more plus. −6.00 becomes −5.50, for example, and +6.00 becomes +6.50. The calculator applies this to each principal meridian, so for toric values sphere and cylinder are converted separately.
Cylinder notation
Ophthalmologists often write astigmatism as a plus cylinder, opticians and lens manufacturers as a minus cylinder. Both describe the same correction. The calculator recognises a plus cylinder by its sign and transposes it: sphere plus cylinder becomes the new sphere, the cylinder changes sign and the axis turns by 90 degrees.
The grid of available values
Contact lenses are not made in every value. Powers come in quarter steps up to ±6.00 and half steps above, cylinders usually only as −0.75, −1.25, −1.75 and −2.25, axes in 10-degree steps. If a glasses value sits exactly between two steps, the calculator shows both and leaves the decision to the fitting. A cylinder up to −0.50 is usually not corrected with a toric lens at all; half of it is folded into the power instead.
What only a fitting provides
Two values are missing from every glasses prescription: the base curve (BC) and the diameter (DIA) of the lens. They depend on the curvature of your cornea and are measured at the fitting. Whether your eyes tolerate lenses and whether the converted power really gives sharp vision also only shows there. The values from this calculator are therefore a guide for the conversation with your optician, not a replacement for it. In the UK, contact lenses may only be supplied against a valid contact lens specification.
Marco Pöhler
Marco Pöhler is the managing director and founder of Kontaktlinsen-Preisvergleich GmbH. He helps people always get their contact lenses at the best price. He also writes about technology and contact lenses on Medium.Frequently asked questions
Can I just order contact lenses with my glasses values?
No. Your glasses values are a good starting point, but contact lenses also need a base curve and diameter, which only a fitting provides. The fitting also checks whether the converted power really works and whether your eyes tolerate lenses.
My prescription uses a plus cylinder. What now?
Ophthalmologists often write astigmatism as a plus cylinder, opticians and lens manufacturers as a minus cylinder. Both describe the same correction. The calculator transposes it: sphere plus cylinder becomes the new sphere, the cylinder changes sign, the axis turns by 90 degrees.
What do LOW, MEDIUM and HIGH mean for the addition?
Many multifocal lenses are not made in every addition value but in two or three bands. Which band matches your reading addition is set by the manufacturer, for example LOW up to +1.25, MEDIUM up to +2.00 and HIGH above. The results show the band per product.