To measure penis length accurately, you need a ruler or measuring tape and a full erection. Place the ruler along the top of the shaft, press the end firmly against the pubic bone, and read the measurement at the tip. This “bone-pressed” method is the same one used in clinical studies and gives the most consistent, comparable result.
How to Measure Length
Start with a full erection. Partial erections will give you a shorter and less consistent number every time you measure. Stand upright or stand against a wall for a consistent posture.
Place a rigid ruler or straight measuring tape along the top of your penis, not the side or underside. The starting point is the base where the shaft meets your body, right at the pubic bone. Press the ruler firmly into the pubic bone so it pushes past any fat pad or pubic hair at the base. This is called the “bone-pressed” measurement, and it matters because the fat pad can hide a significant portion of the shaft. Without pressing in, two people with identical anatomy but different body compositions would get very different numbers.
Read the measurement at the very tip of the glans. That number is your bone-pressed erect length, the standard used in virtually all published research on penis size.
How to Measure Girth
Girth is the circumference of the shaft. You’ll need a flexible tailor’s tape or a piece of string. With a full erection, wrap the tape around the thickest part of the shaft (for most men, this is the midshaft area). If you’re using string, mark where it overlaps, then lay it flat against a ruler to get the number.
Keep the tape snug but not compressing the skin. One consistent wrap, no overlap, no gaps. If your shaft varies noticeably in thickness along its length, you can measure at multiple points, but the midshaft measurement is the one most studies use for comparison.
What the Averages Actually Are
A large meta-analysis published in BJU International pooled data from 17 studies covering over 15,500 men, all measured by healthcare professionals using standardized methods. The results: the average erect length was 13.12 cm (about 5.16 inches), and the average erect circumference was 11.66 cm (about 4.59 inches).
Those numbers are notably smaller than what you’ll often see cited online. That’s because self-reported measurements consistently run higher than clinician-measured ones. Research in Psychology of Men & Masculinity found that self-reported averages landed around 6 inches (15.2 cm) for erect length, while carefully controlled studies where researchers induced and measured erections came in at a mean of 5.3 inches (13.5 cm). The gap is about three-quarters of an inch, likely a combination of rounding up, inconsistent technique, and optimistic measuring.
If your number falls anywhere in the general neighborhood of these averages, you’re statistically normal. The clinical threshold for a micropenis in adults is a stretched length below roughly 9.3 cm (about 3.7 inches), which represents 2.5 standard deviations below the mean. This is a specific medical diagnosis, not a casual label.
If You Can’t Measure While Erect
The stretched flaccid method is a reasonable alternative. Gently stretch the flaccid penis to its full extent and measure from the pubic bone to the tip, using the same bone-pressed technique described above. Research published in The Journal of Urology found that stretched flaccid length predicted erect length with good reliability (R² of 0.79), meaning the two measurements track closely for most men. Clinicians routinely use this method when an erection isn’t practical.
Regular flaccid length without stretching is far less reliable. The same study found a much weaker correlation between resting flaccid length and erect length (R² of 0.68). Flaccid size fluctuates heavily with temperature, arousal, stress, and blood flow, making it a poor stand-in for erect size.
Common Mistakes That Skew Results
- Measuring from the side or underside. The underside of the shaft follows a curve and includes the frenulum area, which inflates the number. Always measure from the top (the dorsal surface).
- Not pressing to the bone. Skipping the bone press can shave off anywhere from a quarter inch to over an inch depending on body fat. Clinical studies always use the bone-pressed method, so if you want a meaningful comparison, you need to do the same.
- Measuring with a partial erection. Erection quality varies day to day. Measure at full hardness for consistency. If you measure multiple times, your largest consistent reading at full erection is the most accurate.
- Using a curved ruler on a curved penis. If your penis has a noticeable curve, a flexible tape along the top surface following the curve will give a slightly longer number than a straight ruler. Most studies use a rigid ruler, so for comparison purposes, a straight-line measurement from base to tip is the standard.
Why Measurement Technique Matters
The reason clinicians and researchers are so specific about technique is that small variations in method produce meaningfully different numbers. Pressing versus not pressing, top versus side, full erection versus partial: each of these can shift the result by enough to move someone from “below average” to “above average” on paper. If you’re measuring out of curiosity or for a practical reason like ordering a correctly sized condom, consistency is what matters most. Pick one method, do it the same way each time, and that’s your number.