Find the size range you should be shopping in, and check any specific frame before you order it — including the part most shops never mention: a bigger frame makes your lenses thicker.
Read the numbers on the inside of your temple arm — they look like 52□18-145. Only use a pair that actually fits you well.
Measure temple-to-temple across the widest part of your face, roughly at eye level. Use the on-screen ruler below if you don't have a tape measure.
| Measurement | Your range | Meaning |
|---|
| Check | Result | Verdict |
|---|
Hold any standard bank card, ID-1 or credit card flat against your screen (its short edge against the dashed outline is easiest to judge) and drag the slider until the outline matches the card exactly. Card width: 85.60 mm.
Almost every frame is stamped A□B-C — for example 52□18-145.
The total width of the frame front is roughly 2 × A + B + endpieces, where each endpiece is about 4–6 mm. That total is the number that decides whether it fits your head.
| Build | Face width (temple to temple) | Lens width A | Temple length |
|---|---|---|---|
| Narrow | under ~129 mm | 50 mm and under | 135–140 mm |
| Medium | ~130–139 mm | 50–54 mm | 140–145 mm |
| Wide | ~140–150 mm | 54–56 mm | 145–150 mm |
| Extra wide | over ~150 mm | 56 mm and up | 150 mm + |
| Face shape | Usually flattering | Usually fights you |
|---|---|---|
| Round | Angular, rectangular frames with a wider top line | Small round frames — they exaggerate the roundness |
| Square | Round or oval frames, thin rims, curved browline | Heavy boxy frames |
| Oval | Almost anything; keep the frame width close to face width | Frames much wider than the face |
| Heart / inverted triangle | Bottom-heavy frames, thin rims, light colours | Top-heavy or heavily decorated browlines |
| Oblong | Deeper lens heights, strong horizontal lines | Shallow, narrow lenses |
Start from the total frame width, not the lens size: aim for a frame front a few millimetres wider than your face at the temples. If your face measures 145 mm, look for frames whose total width lands around 147–153 mm — typically eyesize 54–56 with a bridge of 17–19. Anything more than about a finger width wider than your face starts to slide and to look oversized.
Look for eyesize 47–50 with a bridge of 16–18, giving a total front around 125–133 mm, and temples of 135–140. Kids' and "petite" lines usually carry these; adult small frames also exist but are less common, so it's worth filtering online shops by frame width rather than by lens size.
The frame should stay put when you look down and when you smile, without pressing on the sides of your head or leaving marks on your nose. If it touches your cheeks when you smile, it is too big. If the temples bow outward noticeably at the hinges, it is too narrow — the frame is being forced open.
Yes, significantly. Lens edge thickness grows with the distance from your optical centre to the far edge of the lens, and that distance is A/2 plus the decentration — which depends on A and B against your PD. Choosing an eyesize 4 mm smaller can take a whole millimetre off the edge of a high-minus lens. Run your numbers in the thickness calculator with two different frame sizes and compare.
Then your eyes sit far from the centre of each lens, which increases edge thickness and can introduce unwanted prism. Keep A + B within about 10 mm of your PD for a comfortable, cosmetic result. Larger differences are still makeable but they cost thickness and, with strong prescriptions, visual comfort.
Lens Thickness Calculator & Visualizer
See exactly how thick your lenses end up in this frame, across every material, with a to-scale cross-section.
High-Index Comparison: 1.50 vs 1.60 vs 1.67 vs 1.74
Thickness, weight and Abbe value side by side — including where the extra money stops buying anything.
Not medical advice. This tool applies fitting rules of thumb and optical geometry. It does not measure, diagnose or correct vision, and it cannot replace a fitting by an optician — especially for children, high prescriptions or progressive lenses.
LensCrunch — optical tools for people who care about the maths.