Fit & Strength Guide
Buying glasses online comes down to two questions: will they fit, and — for readers — what strength do I need? This page answers both in a couple of minutes.
Part 1 — Frame measurements
Most frames have three numbers printed on the inside of one temple arm, in millimetres. They usually look like 50–18–140.
| Number | What it is | Typical range |
| 1st | Lens width — one lens at its widest point | 40–60 mm. Under 50 is small, 51–54 medium, 55+ large |
| 2nd | Bridge — the gap that sits on your nose | 14–24 mm. Narrower nose, smaller number |
| 3rd | Temple length — the arm, hinge to tip | 120–150 mm. 140 and 145 are the most common |
Some frames add a fourth number, which is lens height.
The easiest way to find your size
Pick up a pair you already own and like the fit of, and look on the inside of the left arm. Those three numbers are your baseline. Anything within about 2 mm of them will feel familiar on your face.
If you have no pair to measure, start from the total frame width instead — roughly the distance across your face from temple to temple. A frame noticeably wider than your face slides down; noticeably narrower pinches.
A quick check once they arrive
- Your eyes should sit near the centre of each lens, not close to the inner edge.
- The frame should not rest on your cheeks when you smile.
- The arms should reach your ears without pressing, and the frame should stay put when you look down.
Part 2 — Choosing reading glasses strength
Reading glasses are sold in dioptres, from about +0.75 to +3.50, in 0.25 steps. Near vision changes gradually for most people from around age 40, so age gives a reasonable starting point.
| Age | Common starting strength |
| 40–44 | +0.75 to +1.00 |
| 45–49 | +1.00 to +1.50 |
| 50–54 | +1.50 to +2.00 |
| 55–59 | +2.00 to +2.25 |
| 60 and over | +2.25 to +2.75 |
Two rules worth knowing. First, when you fall between two strengths, take the lower one — over-correcting near vision is more tiring than under-correcting it. Second, hold your reading material where you actually read it, usually around 35–40 cm, and judge from there; testing at arm's length gives a misleading answer.
Please read this part. The table above is a starting point, not a diagnosis. Individual eyes vary a lot — two people the same age can need strengths a full step apart, and one eye can differ from the other. Ready-made reading glasses use the same strength in both lenses and do not correct astigmatism. If your vision has changed noticeably, if one eye is clearly different from the other, or if you get headaches or eye strain while reading, see an optometrist rather than working it out from a chart. An eye exam checks for things reading glasses cannot fix.
Part 3 — What we do and don't do
LUMIÈRE sells frames, ready-made reading glasses, blue light and sun eyewear. We do not fill prescriptions — we cannot fit lenses made to your own prescription, and we do not sell contact lenses.
Every order is covered by our 30-day guarantee. If a pair arrives damaged or turns out to be the wrong fit, contact us and we will sort it out — in most cases without asking you to ship anything back.
Still unsure which size or strength to order? Message us through the contact page with the numbers from a pair you own, and we will tell you which of ours comes closest. A real person replies within 24 hours.