Accurate erect circumference beats guessing from marketing labels. Nominal width is how manufacturers describe ring size; a 2 mm mismatch can mean slip or breakage. Use the calculator, then read the mm on the SKU — not only words like “Magnum” or “XL.”

Measurement checklist

• Measure at full erection; average two readings
• Tape around the widest shaft point, parallel to the body
• String method: mark overlap, lay flat, measure with a ruler
• Length: pubic bone pressed to tip — secondary to girth for NW

Example brands by band

Limitations

• Nominal width on the box is the flat width, not rolled circumference — brands round differently
• Latex stretch varies; you may prefer ±1 mm NW from the calculated target for comfort
• Length matters less than girth for most straight condoms (extra length rolls at the base)
• Oil-based lube degrades latex; use water- or silicone-based lubricant only
• This tool does not replace STI testing, partner communication, or medical advice

Sources