How-to · Educational fit guide · Updated October 2, 2026
How do I know my condom size?
Direct answer
Condom size is the nominal width in millimeters on the box. It equals erect girth in millimeters divided by 2. A 4.5 inch girth is 114 mm around, so the unstretched match is 57 mm (Large). Length does not pick the size. Most pharmacy condoms are 52–54 mm.
Formula
Nominal width is the condom laid flat. Unstretched circumference is about twice that width, so:
nominal width (mm) = girth (mm) ÷ 2
Inches × 25.4, or centimeters × 10, gives girth in millimeters. Worked example: 4.5 × 25.4 = 114.3 mm, and 114.3 ÷ 2 = 57.1 mm, which rounds to 57 mm. Veale et al. (BJU International, 2015) reported a mean erect circumference of 11.66 cm (4.59 in). That girth is an unstretched match of about 58 mm, wider than a typical 52–54 mm pharmacy condom. Latex stretches, so many people are still comfortable a few millimeters under the unstretched number.
Citeable examples
| Girth | Around | Nominal width | Band |
|---|---|---|---|
| 4 in (10.2 cm) | 102 mm | 51 mm | Regular / Standard |
| 4.5 in (11.4 cm) | 114 mm | 57 mm | Large |
| 5.5 in (14 cm) | 140 mm | 70 mm | Extra Large |
| 4.59 in (11.7 cm) | 117 mm | 58 mm | Extra Large |
Full inch and centimeter table, plus a reverse lookup from the box width: condom size chart by girth.
How to measure
- Measure when fully erect. A flaccid measurement undersizes the condom.
- Wrap a soft tape, or a strip of paper you then measure with a ruler, around the thickest part of the shaft.
- Take two readings and average them. Do not pull the tape tight enough to dent the skin.
- Convert to millimeters (inches × 25.4, or cm × 10) and divide by 2.
- Buy the package whose printed nominal width is nearest that number. Ignore clothing-style words if they disagree with the millimeter.
Fit bands used on this site
| Fit | Nominal width | Girth (unstretched) |
|---|---|---|
| Snug / Slim | 0–47 mm | under 3.7" |
| Regular / Standard | 47–52 mm | 3.7"–4.09" |
| Large | 52–58 mm | 4.09"–4.57" |
| Extra Large | 58+ mm | over 4.57" |
Limits
- This is an unstretched match. A condom a few millimeters narrower can still fit because latex and polyisoprene stretch.
- Flared condoms print a base width. Trojan lists Magnum Original at 55 mm base (about 62 mm mid-shaft) and Magnum XL at 58 mm base (about 63 mm mid-shaft).
- The same brand name is a different millimeter in the US than in the UK or EU. Read the box you can buy.
- Oil-based products damage latex. Use water- or silicone-based lubricant. This page is not medical advice and does not replace STI testing.
Use the free calculator
Enter girth in inches, centimeters, or millimeters: Condom size calculator. Sources used for the numbers on this page include Veale et al., BJU International (2015), the WHO condoms fact sheet, and CDC condom-use guidance.