To measure girth, wrap a flexible measuring tape or a strip of paper around the shaft of your fully erect penis at its midpoint, then read or mark where the material overlaps. The number you get is your circumference. Most people fall between 4 and 5 inches, which corresponds to standard condom sizing.
What You Need
A soft, flexible tailor’s measuring tape is the easiest tool. If you don’t have one, a strip of paper, a piece of string, or even a shoelace works. Wrap it around the shaft, mark where it meets itself, then lay it flat against a rigid ruler to get your measurement in inches or centimeters.
Avoid using a rigid ruler directly. It can’t conform to a curved surface, so you’ll get an inaccurate number no matter how carefully you try.
Where to Measure
The standard spot is mid-shaft, roughly halfway between the base and the tip. This is the measurement that condom manufacturers use for sizing and the one most referenced in clinical research. If your shaft varies noticeably in thickness along its length (which is normal), take a second measurement at the base as well. The thickest point is the one that matters most for condom fit.
Why You Need a Full Erection
Flaccid size does not reliably predict erect size. Research published in the Journal of Urology confirmed that neither age nor flaccid dimensions accurately forecast erect measurements. The correlation between flaccid and erect states simply isn’t close enough to be useful. Blood flow during arousal changes both length and circumference substantially, and the degree of change varies from person to person. A girth measurement taken at partial arousal will be smaller and inconsistent if you try to repeat it.
Wait until you’re fully erect before wrapping the tape. If you lose your erection partway through, start over rather than estimating.
Getting a Consistent Reading
Even in clinical settings, penile measurements are surprisingly hard to standardize. A 2025 review in Oxford Academic noted that professional urology guidelines offer limited practical guidance on measurement technique, and clinicians often rely on local practices that vary from one office to the next. That variability applies at home, too, so consistency in your own method matters more than hitting some “official” protocol.
Keep these points in mind:
- Tape tension: Pull the tape snug against the skin without compressing the tissue. If you’re squeezing hard enough to create an indent, you’re pulling too tight. If the tape is loose enough to slide freely, it’s too loose.
- Angle: Keep the tape perpendicular to the shaft, not angled or spiraling. A diagonal wrap adds extra length to the measurement.
- Repeat it: Measure on two or three separate occasions, ideally on different days, and average the results. Erection firmness varies with arousal level, time of day, hydration, and other factors. A single measurement is a snapshot, not a reliable number.
- Stand or sit the same way each time: Body position can subtly change how blood distributes. Pick one position and stick with it across sessions.
How Girth Relates to Condom Fit
Girth is actually more important than length for choosing the right condom. A condom that’s too tight can feel uncomfortable and is more likely to break. One that’s too loose can slip off. Cleveland Clinic lists standard condoms, such as the regular Trojan size, as appropriate for a girth of 4 to 5 inches. If you measure below that range, look for snug or slim-fit options. Above 5 inches, large or XL sizes will be more comfortable and secure.
Most condom brands list a “nominal width” on the box, which is the flat width of the condom laid on a table. To compare that number to your girth, divide your circumference by 2. If your girth is 4.7 inches, for example, you want a nominal width close to 2.35 inches (about 60 mm). A little stretch is built in, so you don’t need an exact match, but getting within a few millimeters makes a noticeable difference in comfort.
Converting Circumference to Diameter
Some sizing guides and products list diameter instead of circumference. To convert, divide your girth by 3.14 (pi). A 5-inch circumference, for instance, equals roughly 1.6 inches in diameter. This conversion assumes a roughly circular cross-section. Most penises aren’t perfectly round, so treat the number as an approximation, which is fine for practical purposes like choosing a product size.