How to Choose the Right Frame Size — Your PD, Width & Bridge Measurements
Buying glasses online means you can't try them on first — but frame measurements eliminate the guesswork. Once you know three numbers printed inside every frame and your PD, you can pick frames that fit the first time. We ordered 12 frames across different sizes to map exactly how these numbers translate to real fit.
The 3 Frame Measurements — Reading the Numbers Inside Your Temple
Look at the inside of any glasses arm. You'll see three numbers, like 52 □ 18 140. Here's what each means:
Lens Width (e.g. 52mm)
The horizontal width of one lens at its widest point. This is the single most important number. 48–52mm fits small/narrow faces. 53–55mm fits medium faces. 56mm+ fits wide faces. A 2mm difference is noticeable — don't round up.
Bridge Width (e.g. 18mm)
The distance between the two lenses across your nose. 16–18mm fits most people. 19–21mm suits wider nose bridges or low nose bridges that need more clearance. Too narrow and the glasses sit too high. Too wide and they slide down.
Temple Length (e.g. 140mm)
The arm length from hinge to tip. 135–140mm for smaller heads. 140–145mm for average. 150mm+ for larger heads. The temple should extend about 40mm past your ear bend. Curved tips (the bent part behind your ear) add grip — straight temples need to be longer.
How to Measure Your PD (Pupillary Distance) — 3 Methods
Method 1: Ask Your Eye Doctor (Most Accurate)
Your PD is part of your medical record. After your exam, ask the optometrist to write it on your prescription. Some offices omit it intentionally to make online ordering harder. If they refuse, remind them it's your data — they are legally required to provide it upon request.
Method 2: Use a Retailer's Online Tool (Free, ±1mm Accuracy)
Fytoo and Zenni both have free web-based PD measurement tools. You hold a standard-size card (credit card, driver's license) against your forehead and take a photo. The software calculates your PD from the reference object. Results are usually within 1mm of an optician's measurement.
Method 3: Mirror + Ruler (Free, ±2mm Accuracy)
Stand 8 inches from a mirror. Hold a millimeter ruler across your brow. Close your right eye, align the 0mm mark with the center of your left pupil. Close your left eye, open your right — read the number aligned with your right pupil center. Repeat 3 times and average. Adult PD typically ranges from 54–68mm for women and 58–72mm for men.
Face Width ↔ Frame Size Matching Table
| Face Width | Total Frame Width | Lens Width Range | Bridge Range |
|---|---|---|---|
| Narrow (120–128mm) | 118–125mm | 48–50mm | 16–18mm |
| Medium (129–138mm) | 125–135mm | 50–53mm | 17–19mm |
| Wide (139–150mm) | 135–145mm | 53–56mm | 18–21mm |
Virtual Try-On Tools — How They Compare
| Retailer | Tool Type | Accuracy | Shows Size? |
|---|---|---|---|
| Fytoo | Photo upload + face scan | Good | ✅ Yes |
| Zenni | Webcam live try-on | Good | Partial |
| Warby Parker | App-based AR | Excellent | ✅ Yes |
| EyeBuyDirect | Photo upload overlay | Fair | ❌ No |
Even with good measurements, there's a 15–20% chance your first pair won't fit perfectly. That's why the return policy matters. Fytoo's 30-day free return window means you can order, try on at home, and exchange if the frame size is off — at no cost. Our testing found that matching your current frame's measurements is the single most reliable predictor of good fit.
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