Explore with clarity with a prescription Snorkeling dive mask

A Comprehensive Guide to Choosing the Correct Lenses for Underwater Vision:

At Oceans Optics, the goal is simple: clear, comfortable vision in a diving mask with prescription lenses. Choosing the right power for your prescription snorkel mask or prescription scuba mask starts with understanding how light behaves underwater and how to read your glasses prescription.

Start with your prescription (SPH only)

Use the Sphere (SPH) value for each eye.

Negative (−) SPH = nearsighted (myopia)
Positive (+) SPH = farsighted (hyperopia)
*Stock mask lenses are spherical, so ignore Cylinder/Axis (astigmatism) for off-the-shelf options.

Why underwater needs a slightly weaker lens

Water + mask create a virtual image that looks ~25–33% closer/larger. To match this underwater magnification—and avoid over-correction—use a slightly weaker power than your glasses.

Simple adjustment we recommend:
Reduce your glasses SPH by 0.50 to 0.75 diopters (toward zero), then choose the nearest 0.50 step we stock.

Quick examples (nearsighted)

OD (Right): SPH −3.00 → Choose −2.50 (−0.50) or −2.25/−2.00 if you prefer a softer, long-day feel—pick the nearest step available.
OS (Left): SPH −2.75 → Choose −2.25 (−0.50) or −2.00 (−0.75); select the closest stocked step (−2.50 or −2.00) if 0.25 steps aren’t offered.

Rule of thumb: pick −0.75 for longer sessions to reduce eye strain; pick −0.50 for shorter swims or extra-crisp distance (gauges, photos).

Final checks

Choose each eye individually (L/R powers can differ).
Prioritize a good mask fit (S/M vs M/L, soft silicone skirt, tempered glass) so your chosen power performs as intended.
Have significant astigmatism or special requirements? Consider custom lenses or speak with your eye care professional.

Swim into clarity with Oceans Optics prescription lenses—built for relaxed, sharp underwater vision on every trip.

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Mask sizing: Mask Size Guide Helper

How to Measure Your Face for a Prescription Snorkel & Scuba Mask

Buying a mask online can be tricky — so we built multiple ways to check fit and feel confident the seal will be just perfect.

1

Measure Width

Outer eye corner to outer eye corner in a straight line (don’t wrap).

2

Measure Height

From just under your nose to just above your eyebrow line.

3

Optional: Head Size

Wrap a string around your hat line, mark, then measure. Use the table as a guide.

4

Enter Your Sizes

Use our slider tool to enter your measurements & find your perfect fit.

How to measure your face for a prescription mask

Quick Face-Size Checker

Tips: use a straight ruler (don’t bend it), check in a mirror, or ask a friend to help.

3 Head-Size Checker (Optional)

Measure around the hat line (above ears/brows)

Head-Size to Mask-Size

Measure your head the same way you’d measure for a hat. Use a soft tailor’s tape (or wrap a piece of string/cord), around your head above the ears and just above the eyebrows, then read the length (or measure the string). Keep it level all the way around.

4 Enter Your Sizes
Use the slider to find your perfect fit!
Underwater Lens Calculator

Underwater, light bends differently and can make your usual prescription feel too strong.
We lower it slightly to prevent overmagnification and keep your vision clear.
Step 1: Enter your prescription to determine your recommended underwater vision

Choose the sign first:
Use for myopia, + for hyperopia.
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Suggested Lens Strength:

Right
Left