Frame Size & Fit Calculator
Read the eye-size, bridge, and temple numbers off any frame, add your PD, and see whether it runs true, wide, or narrow before you buy.
Fit estimate
A workable fit. The small decentration is well within what a lab handles routinely; lenses will be centred to your PD.
Matching a frame to your face by the numbers
Buying glasses online means the frame is just three numbers and a picture. Those numbers are more useful than they look: eye size plus bridge gives the distance between the lens centres, and comparing that to your pupillary distance tells you whether the optics will fall in front of your eyes or off to the sides. A frame whose centres sit far from your pupils forces the lab to shove the optics inward, which thickens lenses and can nudge in unwanted prism.
The lens span — twice the eye size plus the bridge — is the horizontal reach of the two lenses and a quick check that a frame isn't simply too big or too small for your face. Read a well-fitting pair you already own for a reference, then use this tool to shortlist new frames in the same range.
Frequently Asked Questions
What do the three numbers on my frame mean?
Frames carry three measurements in millimetres, often printed inside a temple as something like 52▢18-140. The first is the eye size (lens width), the middle is the bridge or DBL (the gap between lenses), and the last is the temple length (the arm that reaches your ear). Together they describe how wide and long a frame is.
What is 'frame PD' and how does it relate to my PD?
The frame PD is the distance between the two lenses' optical centres, and it equals eye size plus bridge. For the best fit it should be close to your own pupillary distance so the optical centres sit in front of your pupils. When the two differ, the lab must decentre the lenses — shift the optics sideways — which this tool quantifies.
What does decentration tell me?
Decentration is how far each lens's optical centre has to move to line up with your pupil, equal to half the gap between frame PD and your PD. Small amounts are routine. Large amounts (roughly over 4–5 mm per eye) push you toward thicker, heavier lenses and, if the frame is very off, harder-to-centre optics — a sign the frame is a poor size match.
Does a bigger frame always mean a worse fit?
Not necessarily — it depends on how the eye size and bridge combine relative to your PD. A wide face with a large PD may fit a big frame perfectly, while the same frame overwhelms a narrower face. The calculator compares your PD to the frame's centres rather than judging size alone.
Can this replace trying frames on?
No. It estimates the optical fit from the numbers, but comfort also depends on nose shape, cheek clearance, ear position, and temple curve. Use it to shortlist sensible sizes, then try frames on and let an optician confirm the fit and adjust them.
Educational estimate based on frame geometry and PD. Comfort also depends on nose, cheek, and ear fit — try frames on and have an optician adjust them.