Estimate how your glasses sphere power may convert to contact lens sphere power in Australia.
Can I use a glasses prescription to order contact lenses in Australia?
No. A glasses prescription does not include all the details needed to order contact lenses. Contact lenses sit directly on the eye, so your prescription needs extra fitting information such as brand, base curve, diameter, lens type and replacement schedule. If you already have a current contact lens prescription, order using those exact contact lens details.
What details do I need to order contact lenses online in Australia?
Before ordering contact lenses online, check that your contact lens prescription includes the details needed to match the lenses prescribed by your optometrist:
- Brand or lens name: Different brands and materials can fit differently.
- Power / Sphere (SPH or PWR): The lens strength.
- Base Curve (BC): The back curve of the lens.
- Diameter (DIA): The width of the lens.
- Replacement schedule: Daily, fortnightly or monthly.
- Cylinder (CYL) and Axis: Needed for toric lenses if you have astigmatism.
- Addition (ADD): Needed for some multifocal contact lenses.
A standard glasses prescription usually does not include these contact lens fitting details. This calculator can help estimate a possible sphere-power change, but it cannot create a complete contact lens prescription.
Glasses prescription to contacts: why does the power shift?
The difference comes down to vertex distance. Because frame lenses rest roughly 10mm to 15mm away from your face, the light pathways are altered compared to a lens floating directly on your cornea. For minor corrections, the variation is trivial; however, for higher levels of myopia or hyperopia, the effective power must be adjusted via vertex calculations to ensure optimal visual acuity.
What this vertex conversion module estimates
This tool performs a calculation to estimate how back-vertex focal dynamics affect standard sphere values.
The calculations rely strictly on your specified vertex baseline (standardised to an industry-average 12mm reference point) and output steps, rounded to standard 0.25-diopter commercial intervals. Your final clinical evaluation results may vary depending on the practitioner's testing.
What this mathematical model cannot calculate
- Anatomical base curve matching
- Optimal diameter coverage
- Lens material suitability
- Toric lens weight balancing, cylinder, or axis calculations
- Multifocal zone layouts or near addition steps
- Tear film compatibility or eye health suitability indicators
If your prescription contains CYL or AXIS fields
When a glasses prescription lists cylinder and axis markers, it denotes astigmatism. Correcting this may require toric contact lenses, which prevent the lens from rotating on the eye. Simple sphere formulas cannot calculate these complex rotational distributions. Please check with your Australian optometrist for a proper toric lens fitting.
First-time contact lens wearers in Australia
If you are new to contact lenses, book a contact lens fitting with an optometrist before ordering online. Power is only one part of a safe and comfortable fit. Your optometrist will check how the lens sits, moves and feels on your eye.
Can I switch contact lens brands when ordering online in Australia?
Do not change your contact lens brand, material, base curve, diameter or replacement schedule unless your optometrist has confirmed the alternative is suitable. Lenses with the same power can still fit differently, so switching products without advice may cause discomfort, poor vision or eye health issues.
Ready to order from your contact lens prescription?
If you already have a current, unexpired contact lens prescription, you can browse contact lenses online by category:
Shop All Contact Lenses in Australia
Shop Coloured Lenses Australia
Shop Daily Contact Lenses in Australia
Daily Lenses for Astigmatism (AU)
Daily Multifocal Lenses Australia
Shop Fortnightly Disposables (AU)
Fortnightly for Astigmatism Australia
Fortnightly Multifocal Lenses AU
Monthly Lenses for Astigmatism AU
Monthly Multifocal Lenses Australia
Contact Lens Prescription FAQs Australia
Is my glasses prescription the same as my contact lens prescription?
No, they are different. Glasses rest on your frame profile away from your eyes, whereas contact lenses sit directly over your corneas. A contact lens prescription also includes additional parameters, such as brand name, material, base curve, and diameter.
Can I order contact lenses online with only my glasses prescription?
No. In Australia, you must purchase contact lenses with a current, unexpired contact lens prescription. A typical glasses prescription does not outline the essential structural metrics required for contact lenses, such as base curve, diameter, lens type or brand.
What details do I need to order contact lenses online in Australia?
You must reference your contact lens brand or lens name, power readings, base curve measurement, total diameter, lens type and replacement schedule. If you correct for astigmatism, you also need cylinder and axis metrics. For presbyopia correction, an ADD power value is required.
Why does contact lens power differ from glasses power?
Under higher diopter conditions, closing the physical gap between your spectacle lens and your eye surface affects the light's refraction path. Lenses resting directly on the tear film layer must adjust their power matrix to account for the change in vertex distance.
Does this calculator work for astigmatism?
No. This calculation tool does not process toric prescription shifts. If your current script displays CYL or AXIS measurements, use your current contact lens prescription directly or consult an Australian optometrist.
Can I use this calculator for multifocal contact lenses?
No. Multifocal contact lens profiles require intricate progressive-zone mapping and near-addition parameters that cannot be determined by basic vertex formulas. Order these directly using an unexpired contact lens script.