To measure penis size accurately, you need a ruler or flexible measuring tape and a full erection. The standard method, called bone-pressed erect length, involves pressing a ruler against the pubic bone at the base and measuring in a straight line to the tip. This is the same technique used in clinical studies, so it gives you the most comparable and consistent number.
How to Measure Length
Place a rigid ruler or measuring tape along the top of your erect penis, starting where the shaft meets your body. Press the end of the ruler firmly into the pubic bone, pushing past any fat or pubic hair at the base. Then measure in a straight line from that point to the very tip of the head. Pressing into the pubic bone matters because the fat pad in that area can obscure a significant portion of the shaft, especially with weight gain. This “bone-pressed” technique gives you a true structural measurement rather than one that fluctuates with body composition.
If your penis has a noticeable curve, whether natural or from a condition like Peyronie’s disease, use a flexible measuring tape instead of a rigid ruler. Lay the tape along the top surface, following the curve, from the pubic bone to the tip. A rigid ruler held against a curved shaft will undercount your actual length.
How to Measure Girth
Girth is the circumference, the distance around the shaft. Wrap a flexible measuring tape or a piece of string around the thickest part of your erect shaft, typically near the middle. If you use a string, mark where it overlaps, then lay it flat against a ruler to get the number. This measurement is especially useful for finding condoms that fit properly, since width and girth matter more than length when selecting the right size.
To convert girth into width (diameter), divide the girth by 3.14. For example, a girth of 4.7 inches gives a width of about 1.5 inches. Condom sizing varies across brands, so a “regular” from one manufacturer may correspond to “large” from another. A condom that’s too narrow can feel tight and risks breaking, while one that’s too loose can slip off during use.
Why Flaccid Measurements Are Unreliable
Flaccid size is not a useful measurement for comparison because it changes constantly. Cold temperatures cause the muscles in the penis and scrotum to contract, pulling everything closer to the body. Swimming in cold water, a chilly room, or even stress can temporarily reduce flaccid size. Once you warm up, things return to normal. This variability is why researchers rarely use resting flaccid length as a meaningful metric.
Stretched flaccid length is a different story. Clinicians sometimes gently stretch the flaccid penis and measure from the pubic bone to the tip, because this number closely correlates with erect length. A study published in the Journal of Urology confirmed that stretched length is a reliable estimate of erect length, making it useful in clinical settings where inducing an erection isn’t practical. For personal measurement at home, though, measuring while fully erect is simpler and more straightforward.
How Your Numbers Compare to Averages
A large review published in the BJJ of Urology, combining data from over 15,000 men, found the following averages:
- Erect length: 5.16 inches (13.12 cm)
- Erect girth: 4.59 inches (11.66 cm)
- Flaccid length: 3.61 inches (9.16 cm)
- Stretched flaccid length: 5.21 inches (13.24 cm)
These are means, with most men falling within about an inch above or below. The standard deviation for erect length was 1.66 cm (roughly two-thirds of an inch), meaning the vast majority of men measure between about 4.5 and 5.8 inches erect. Self-reported surveys tend to produce higher numbers than clinician-measured studies, so if you’ve seen larger averages elsewhere, measurement bias is the likely explanation.
When Size Falls Outside the Typical Range
A micropenis is a clinical diagnosis with a specific threshold: a stretched length of 2.95 inches (7.5 cm) or less in adults, which falls more than 2.5 standard deviations below average. This is a rare condition, typically identified in infancy, and is distinct from simply being on the smaller end of normal. If your bone-pressed erect measurement is above that cutoff, you fall within the normal range, even if you’re below average.
Tips for a Consistent Measurement
Take your measurement at full erection. Partial erections will give you a shorter number that doesn’t reflect your actual size. If you want to confirm accuracy, measure on a few different occasions, since erection quality can vary with arousal level, fatigue, and time of day. Room temperature matters too: a warm environment helps ensure full blood flow.
Always measure from the top of the shaft (the side facing your belly), not the underside. The underside includes the curve toward the scrotum and will give an inflated reading. Pressing into the pubic bone is standard practice, not cheating. It accounts for the fat pad and gives you the number that matches clinical data. If you want to know your visible or “non-bone-pressed” length, simply place the ruler at the skin surface without pressing in. Both numbers are valid, but bone-pressed is the one used in research and size charts.