Estimate how the sphere power of glasses may convert to the contact lens sphere power.
Can I order contact lenses online with my glasses prescription?
Not usually. A glasses prescription and a contact lens prescription are not always the same. Contact lenses need extra details such as base curve, diameter, lens type and sometimes brand-specific parameters. If you already have a current contact lens prescription, use the exact details listed on that prescription when ordering online.
Do I have enough details to order contact lenses online in NZ?
Before ordering contact lenses online, check that your contact lens prescription includes the details needed for the type of lenses you wear.
- Brand or lens name
- Power / Sphere, sometimes shown as PWR or SPH
- Base Curve, usually shown as BC
- Diameter, usually shown as DIA
- Cylinder and Axis, if you wear toric lenses for astigmatism
- ADD, if you wear multifocal contact lenses
If you only have a glasses prescription, you may not have all the details needed to order contact lenses online. This calculator can help explain the sphere power difference, but it does not replace the full contact lens prescription details used when ordering.
Glasses prescription to contacts: what changes?
Glasses sit in front of your eyes, while contact lenses sit directly on the eye. Because of this difference, higher glasses prescriptions may need a vertex distance adjustment before they are used as contact lens powers. This glasses prescription to contacts calculator gives a sphere power estimate only, not a full contact lens prescription.
What this calculator can estimate
This calculator estimates contact lens sphere power from glasses sphere power using a standard vertex distance adjustment. It is most relevant for higher prescriptions where the distance between glasses lenses and the eye can affect the effective lens power.
The estimate uses the vertex distance selected by the user, defaulting to 12 mm, and rounds calculations to the nearest 0.25D step. Your actual contact lens prescription may differ.
What this calculator does not calculate
- Base curve
- Diameter
- Lens brand or material suitability
- Toric contact lens cylinder and axis
- Multifocal or add power requirements
- Whether contact lenses are suitable for your eyes
If your prescription includes CYL or AXIS
If your glasses prescription includes cylinder or axis values, you may need toric contact lenses. Toric lenses are not converted using a simple sphere-only calculator. Use your current contact lens prescription or ask an optometrist before ordering.
First-time contact lens wearers
If you have not worn contact lenses before, book a contact lens fitting before ordering online. Power alone is not enough to choose contact lenses safely, because fit, comfort, base curve, diameter and lens suitability also matter.
Ready to order from your contact lens prescription?
If you already have a current contact lens prescription, you can browse contact lenses online by category:
- Browse All Contact Lenses
- Daily Disposable Lenses
- Fortnightly Disposables
- Monthly Disposable Lenses
- Astigmatism / Toric Lenses
- Multifocal / Presbyopia Lenses
- Coloured Contact Lenses
Contact Lens Prescription FAQs
Is my glasses prescription the same as my contact lens prescription?
No, not always. Glasses sit in front of your eyes, while contact lenses sit directly on your eyes. Contact lens prescriptions may also include base curve, diameter, lens brand and lens type.
Can I order contact lenses online with only my glasses prescription?
Usually, you should order contact lenses using a current contact lens prescription. A glasses prescription may not include fitting details needed for contact lenses, such as base curve, diameter, lens type or brand.
What details do I need to order contact lenses online?
You usually need your contact lens brand or lens name, power, base curve and diameter. If you wear toric lenses, you may also need cylinder and axis. If you wear multifocal lenses, you may also need ADD.
Why does contact lens power differ from glasses power?
For stronger prescriptions, the distance between glasses lenses and your eyes can change the effective power. Contact lenses sit directly on the eye, so the power may need to be adjusted.
Does this calculator work for astigmatism?
This calculator does not calculate toric contact lens prescriptions. If your prescription includes CYL or AXIS, use your current contact lens prescription or ask an optometrist.
Can I use this calculator for multifocal contact lenses?
No. Multifocal contact lenses require additional prescription details, including add power, and should be ordered from a current contact lens prescription.