To measure your penis accurately, you need a full erection, a flexible measuring tape (or a piece of string and a ruler), and a consistent technique. The two measurements that matter are length and girth, and each requires a slightly different approach. Getting reliable numbers takes about two minutes once you know the method.
How to Measure Length
Stand upright with a full erection. Place a ruler or measuring tape along the top of your penis, starting where the shaft meets your body at the pubic bone. Press the end of the ruler firmly into the pubic bone, pushing past any fat pad or pubic hair. Measure in a straight line to the tip. This “bone-pressed” method is the same one used in clinical studies, and it gives the most consistent result because it isn’t thrown off by differences in body weight or fat distribution.
If your penis curves noticeably to one side or up/down, a rigid ruler won’t follow the curve and will undercount. Use a flexible measuring tape instead, laying it along the top surface and following the curve from base to tip. This gives you the functional length rather than a straight-line shortcut across the curve.
How to Measure Girth
Girth is the circumference, the distance around the shaft. Wrap a flexible measuring tape snugly (not tightly) around the thickest part of the shaft while fully erect. For most people, the thickest point is just below the head, though it can vary. If you don’t have a measuring tape, wrap a piece of string or a strip of paper around the shaft, mark where the ends meet, then lay the string flat against a ruler. Clinical studies typically measure at the middle of the shaft, but for personal reference the thickest point is more practical and more commonly cited.
Getting a Reliable Number
A single measurement on a single day isn’t particularly reliable. Erection quality fluctuates based on arousal level, stress, time of day, and even room temperature. Cold environments can noticeably reduce size, so measure in a comfortably warm room when you’re fully aroused. Take measurements on three separate occasions and average the results. This smooths out the normal day-to-day variation and gives you a number you can trust.
Some flexible measuring tapes have slight stretch to them. Pull it just snug enough to make contact all around without compressing tissue. If you’re using a cloth sewing tape, this is rarely an issue, but the cheap plastic ones that come in toolkits can stretch and give inflated girth readings.
What About Flaccid Measurements?
Flaccid size varies so much from hour to hour that it’s not a particularly useful number. If you do want one, the more reliable version is the “stretched flaccid length.” Place one hand flat above the base of your penis, hold the head between thumb and forefinger with the other hand, and gently extend the penis forward until it’s fully stretched but not uncomfortable. Measure from the pubic bone to the tip. This number correlates more closely with erect length than a resting flaccid measurement does, and it’s the measurement some surgeons use when planning procedures like penile implants.
How You Compare to Averages
The largest systematic review on the topic, published in BJU International and covering over 15,000 men, found the following averages for erect measurements:
- Erect length: 13.1 cm (5.2 inches), with most men falling between 11.5 and 14.8 cm (4.5 to 5.8 inches)
- Erect girth: 11.7 cm (4.6 inches), with most men falling between 10.5 and 12.7 cm (4.1 to 5.0 inches)
“Most men” here means roughly 68% of the population, one standard deviation in either direction from the mean. If your numbers fall anywhere in those ranges, you’re squarely in the middle of the bell curve. A separate meta-analysis in the World Journal of Men’s Health reported a pooled mean erect length of 13.9 cm (5.5 inches), slightly higher, likely reflecting differences in which studies were included and how measurements were taken.
One thing worth knowing: men consistently overestimate their size when self-reporting compared to clinician-measured studies. The studies cited above used trained clinicians doing the measuring, so if your self-measured number is close to these averages, you’re genuinely typical.
Common Mistakes to Avoid
Measuring along the underside of the shaft gives a longer number because the underside curves further from the pubic bone. The standard is always along the top (the dorsal surface). Starting your measurement from the side of the shaft rather than the top is another common source of inconsistency.
Not pressing into the pubic bone is probably the most frequent error. The fat pad above the base can hide a meaningful amount of length, sometimes a centimeter or more. Pressing the ruler to the bone doesn’t inflate your measurement; it just removes a variable that would otherwise change with weight fluctuations.
Finally, measuring at partial erection will undercount both length and girth. If you lose your erection mid-measurement, start over. The goal is peak rigidity for a number that’s consistent and comparable to published averages.