Every eyeglass frame — including every frame Aldermiller sells — is built to four precise measurements, all in millimeters. Once you know what they mean, comparing your current glasses to anything in our catalog takes about thirty seconds. Here's the full breakdown, including the one measurement that matters most if you wear progressive lenses.
Where to Find It, and How to Read It
Look on the inside surface of one temple arm — the part that rests behind your ear, facing your head when the glasses are worn. You'll usually find a short string of numbers, something like 52▭18-140, sometimes separated by dashes and sometimes by a small square icon in place of one of the dashes.
How to read the code printed inside your temple arm
Worked example: if your current glasses are stamped 52-18-140 inside the temple, that breaks down as:
● 52 — your lens width (A): each lens is 52mm wide at its widest point
● 18 — your bridge width (DBL): there's 18mm of frame between your two lenses, resting on your nose
● 140 — your temple length: the arm measures 140mm from the hinge to the tip, including the curve behind your ear
Occasionally you'll see a fourth number elsewhere on the arm, separate from the main code — this is lens height (B), covered in its own section below. It's printed less consistently than the other three, since most single-vision frame styles don't require it to be called out.
All Four Measurements, Shown on the Frame Itself
The temple-arm code tells you the numbers, but it helps to see where each measurement actually falls on a pair of glasses. Here's the same four measurements — lens width, bridge width, lens height, and temple length — shown directly on a front-facing frame.
Where each measurement falls on the frame, viewed from the front
Notice that lens width, bridge width, and lens height are all fully visible from the front — you're looking straight at exactly what's being measured. Temple length is the one exception: since the arms fold backward along the sides of your head, only part of that measurement is visible face-on. That's why temple length is read from the printed code rather than estimated visually.
The Four Frame Measurements
|
Measurement |
What It Is |
Typical Range |
|
A — Lens Width |
Horizontal width of one lens at its widest point (also called "eye size") |
40–60mm |
|
DBL — Bridge Width |
Distance between the two lenses, where the frame rests on your nose |
14–24mm |
|
Temple Length |
Length of the arm from the hinge to the tip, including the curve behind your ear |
120–150mm |
|
B — Lens Height |
Vertical height of the lens, from its lowest point to its highest point |
28–45mm, varies widely by frame style |
B-measurement, specifically, is the one worth paying close attention to if you're getting progressive lenses — covered in detail below.
A, DBL, and Temple Length: General Size Categories
There's a widely used industry convention for lens width specifically, which is a reasonable starting point if you don't have a current pair to compare against:
|
Category |
Lens Width (A) |
|
Small |
50mm or less |
|
Medium |
51–54mm |
|
Large |
55mm or more |
|
Bridge width and temple length don't have an equivalent standardized small/medium/large convention the way lens width does — they're better matched directly against a current comfortable pair, within about 1–2mm, than sorted into categories. |
B — Lens Height: The Measurement Progressive Wearers Should Watch Closely
Unlike lens width, there's no single industry-wide small/medium/large convention for lens height — frame styles vary too much for that kind of clean categorization to be meaningful. What is consistently agreed upon, across multiple independent optical sources, is this:
|
A lens height of at least 30mm is generally considered the minimum for progressive (multifocal) lenses to have enough vertical room for all three vision zones — distance, intermediate, and near — to fit properly. Frames with a lens height noticeably below 30mm may not be suitable for progressives at all, regardless of prescription. |
Why this matters: a progressive lens needs enough vertical space to blend three different corrective powers smoothly, from distance vision at the top to reading vision at the bottom. A short, narrow frame — the kind that's stylish for single-vision wear — can genuinely be too small to hold a comfortable progressive prescription well, independent of how good your prescription itself is.
A Reasonable General Reference Range
While there's no official standard the way there is for lens width, here's a general framework worth knowing, based on common frame styles across the market:
● Below 28mm: Not recommended for progressive lenses — very limited usable near-vision area, even with modern lens designs.
● 28–30mm: The minimum workable range for progressives — usable, but with a narrower near-vision zone than most wearers find comfortable.
● 30–38mm: The comfortable working range for most progressive wearers — this covers the majority of standard eyeglass frame styles.
● 38mm+: Generous room for progressives — common in larger, more classically-shaped frames.
This is a general reference, not a precise cutoff — the right fit also depends on your specific segment height and prescription. See our Segment Height Guide for how that number gets calculated for your specific frame.
Aldermiller Frame Measurement Reference
Every product page lists that frame's exact A / DBL / Temple / B measurements in the product description — the fastest way to compare a specific Aldermiller frame against glasses you already own.
How to Use This Guide
● If you have a comfortable current pair: compare all four numbers directly against any Aldermiller product page — matching within 1–2mm on lens width and bridge width, and 2–3mm on temple length, should feel very similar.
● If you're ordering progressives: check the B-measurement on the product page specifically. Look for 30mm or more as a baseline, and more if you know you prefer a generous near-vision zone.
● If you're not sure where to start: email hello@aldermiller.com with your face shape or a straight-on photo, and we're glad to suggest a size range.
For the next step — figuring out your segment height once you've picked a frame — see our companion guide, Frame Size and Segment Height: A Complete Fit Guide.