The standard method uses a ruler or measuring tape pressed against the pubic bone, measuring along the top of a fully erect penis to the tip. This “bone-pressed erect length” is the same technique used in clinical studies, which makes it the most reliable way to compare your measurement to published averages. Here’s exactly how to do it for both length and girth.
How to Measure Length
You’ll need a rigid ruler or flexible measuring tape and a full erection. Partial erections will give you a shorter, inconsistent number, so wait until you’re fully aroused before measuring.
Place the ruler or tape along the top of your penis (the side facing your belly when you’re standing). Press the end firmly into the pubic bone at the base, pushing past any fat pad or pubic hair. This “bone-pressed” technique eliminates body fat as a variable and is the method used in virtually every clinical study on penis size. Measure in a straight line from the pubic bone to the very tip of the glans.
If your penis has a noticeable curve, whether natural or from Peyronie’s disease, a flexible measuring tape will follow the contour more accurately than a rigid ruler. Lay the tape along the top surface and let it bend with the shaft.
How to Measure Girth
Girth is the circumference of the shaft. Use a flexible measuring tape or, if you don’t have one, wrap a strip of paper or string around the shaft and mark where it overlaps, then measure that length against a ruler.
Wrap the tape snugly around the thickest part of the shaft at full erection. For most people this is roughly mid-shaft, though some find the base or area just below the glans is widest. The tape should be firm against the skin but not compressing the tissue. Clinical measurements are typically taken at the base of the shaft, but for practical purposes (like finding a correctly sized condom) measuring at the widest point is more useful.
The Stretched Flaccid Method
If measuring while erect feels awkward or impractical, there’s a clinical alternative. Stretched flaccid length closely predicts erect length, with a statistical correlation strong enough that urologists use it as a stand-in. A study published in The Journal of Urology found that stretched flaccid length predicted about 79% of the variation in erect length, making it a reliable estimate.
To do this, hold the head of your flaccid penis and gently stretch it outward as far as it comfortably goes. Press the ruler into the pubic bone just as you would for an erect measurement, and measure to the tip. The number you get will typically be close to your erect length, though erect measurements remain the gold standard.
Unstretched flaccid length, by contrast, is not a good predictor. Flaccid size varies significantly with temperature, blood flow, and time of day, so it doesn’t correlate well with erect size.
What the Averages Actually Are
A systematic review covering over 15,500 men measured by healthcare professionals found a mean erect length of 13.12 cm (about 5.2 inches) with a standard deviation of 1.66 cm. That means roughly two-thirds of men fall between about 4.5 and 5.8 inches. A separate study of 1,661 sexually active men in the United States reported a mean erect length of 14.15 cm (5.6 inches) and a mean erect circumference of 12.23 cm (4.8 inches). The slight difference between studies reflects variation in measurement methods: the second study involved self-measurement for condom fitting, which can skew results slightly higher.
A more recent meta-analysis pooling global data found a mean erect length of 13.93 cm (5.5 inches), which falls right between those two figures. The takeaway is that the clinical average sits in the range of 5.1 to 5.5 inches, depending on the study.
For context, the clinical threshold for micropenis in adults is a stretched length of 2.95 inches (7.5 cm) or less, which is 2.5 standard deviations below the mean. This is a rare condition, typically identified at birth rather than in adulthood.
Getting a Consistent Result
Penis size fluctuates. Arousal level, stress, room temperature, and even time of day can all affect erection quality, which directly affects your measurement. A single measurement on a single day isn’t necessarily your “true” size. If accuracy matters to you, measure on three or four different occasions over a couple of weeks and average the results.
A few things that improve consistency: measure at full erection (not partial), always press the ruler to the pubic bone, always measure along the top (dorsal) surface, and use the same tool each time. Measuring from the side or underside will give you a different number because of the way the shaft attaches to the body.
Why Bone-Pressed Measurement Matters
The reason every clinical protocol presses the ruler into the pubic bone is simple: the fat pad above the base of the penis varies from person to person and changes with weight gain or loss. Without pressing through it, two men with identical penile anatomy could get different numbers purely based on body composition. Bone-pressed measurement removes that variable entirely, giving you a number that reflects actual penile tissue length rather than how much fat surrounds the base.
If you’ve lost or gained significant weight recently, you may notice your non-pressed measurement changes while your bone-pressed measurement stays the same. The underlying anatomy hasn’t changed, just the amount of tissue covering it.