Glasses to contact lens power calculator
A contact lens sits on the eye, so numbers above ±4.00 change. Enter your glasses number to see the contact lens power.
Glasses to contact lens power
How to use it
- Enter the sphere from your glasses prescription with its sign.
- Add the cylinder and axis if you have them.
- Read the contact lens power, rounded to 0.25.
- Take the result to your fitting.
Your entries stay in your browser. Nothing is sent to us. The result is for information and is not a diagnosis.
The vertex distance formula
Glasses sit about 12 mm in front of the eye. Moving the lens onto the eye changes its effective power: contact lens power = F ÷ (1 − 0.012 × F), where F is the glasses power. For −6.00 this gives −5.60, usually dispensed as −5.50. For +6.00 it gives +6.47, dispensed as +6.50. Each meridian is converted separately when there is a cylinder.
Spherical equivalent
Sphere plus half the cylinder. It is used when a small cylinder is left uncorrected in a plain contact lens.
Transposition
The same prescription can be written with a plus or a minus cylinder. Add the cylinder to the sphere, change the sign of the cylinder, and turn the axis by 90.
See contact lenses at EyeBar Optical and how to read your prescription.
Questions
Is my contact lens number the same as my glasses number?
Below about ±4.00, yes. Above that, minus powers become weaker and plus powers stronger in a contact lens.
Can I order contact lenses with this result?
Use it as a guide. Contact lenses also need a base curve and diameter chosen for your eye.
What is a toric lens?
A contact lens with a cylinder, for astigmatism.
Prepared by the team at Babar Homeopathic Clinic & EyeBar Optical, Kangan Pur. Last updated 3 October 2026. See our medical disclaimer.
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