Ray-Ban RB3721 Square Sunglasses

Most of our frames are “one size,” designed to fit a wide range of faces. A few styles come in multiple sizes. Use your current glasses as the best reference, or follow the quick steps below.

1) How to read frame size (on your glasses)

Look inside the temple (arm). You’ll see numbers like: 52□18–140

• 52 = Lens width (mm)

• 18 = Bridge width (mm)

• 140 = Temple length (mm)

Match these to the new frame for the most reliable fit.

2) Quick fit by face width (no glasses handy?)

Use a ruler (millimeters) across your face at the pupils, or try the “credit-card test” (a card is ~54 mm wide).

Tip: Sunglasses often run 1–2 mm larger than optical frames for a comfortable, slightly looser fit.

3) One-size frames—how to choose

• Compare the listed size to your current frame stamp (e.g., if you wear 52□18–140, look for something close: 51–53 lens, 17–19 bridge, 140–145 temple).

• If between sizes, pick slightly larger for sunglasses and closer match for optical.

• Small adjustments (nose pads, temple bend) by an optician can fine-tune the fit.

4) What each number changes

• Lens width: overall frame width/coverage.

• Bridge: comfort on the nose; higher bridge = more space.

• Temple length: behind-ear comfort; longer temples for larger heads or if temples feel tight/short.

5) Common size examples

• Optical (unisex): 50–54 / 17–19 / 140–145

• Sunglasses (unisex): 52–56 / 16–20 / 140–150

• Smaller faces: start at lens width 48–50

• Larger faces: look at 55–57

6) Still unsure?

• Match your current frame numbers first.

• Check our product photos on model notes (if available).

• You can message us your current size (e.g., 52□18–140) and preferred fit (snug/standard/relaxed)—we’ll suggest options.