To measure your penis with a ruler, place a rigid ruler along the top of the shaft, pressing the end firmly against the pubic bone, and read the measurement at the tip of the head. This “bone-pressed” method is the standard used in clinical research because it accounts for differences in body fat and gives the most consistent, comparable result. Below is a detailed walkthrough of how to get an accurate measurement for both length and girth.
Measuring Erect Length
You’ll get the most accurate length measurement when fully erect. Use a rigid ruler rather than a flexible tape measure, as a rigid ruler was the tool used in roughly 63% of penile measurement studies. Stand upright or stand against a wall for a consistent posture.
Place the ruler along the top (dorsal) surface of the penis, not the side or underside. Press the end of the ruler firmly into the pubic bone just above the base of the shaft. This compresses the fat pad that naturally sits over the pubic bone, revealing the portion of the shaft that’s hidden beneath it. Read the measurement at the very tip of the head. This technique is called a “bone-pressed erect length” measurement, and it’s the one most medical studies use when reporting averages.
If you don’t press the ruler to the bone, you’re taking what’s known as a non-bone-pressed measurement. That number reflects only the visible external length, without compressing any tissue. It’s a valid measurement too, but it will be shorter, and the difference between the two grows larger as body fat increases. If you want to compare your result to published averages, you need to know which method those averages used. Most clinical data is bone-pressed.
Measuring Girth
A ruler alone won’t give you circumference. You need a flexible measuring tape, or a simple workaround: wrap a piece of string or a strip of paper snugly around the thickest part of the erect shaft, typically just below the head. Pinch or mark where the end meets the wrapped portion, then lay that string flat against your ruler. That length is your girth.
Some studies measure circumference at both the base and just below the head, since the shaft isn’t perfectly uniform. If you want a single number, the midshaft or the thickest point is the most commonly reported location.
Stretched Flaccid Length
If measuring while erect isn’t practical, stretched flaccid length is a reliable alternative. Research confirms a strong correlation between stretched flaccid length and actual erect length, close enough that urologists regularly use it in clinical assessments.
To do this, gently grip the head and stretch the flaccid penis outward to its full extent without causing pain. With the ruler pressed to the pubic bone along the top of the shaft, read the measurement at the tip. The result should approximate your erect length, though individual variation exists.
Factors That Affect Accuracy
Room temperature matters more than you might expect. Cold environments cause significant contraction, which can shorten a flaccid measurement noticeably and even affect erection quality. Researchers conducting measurement studies typically work in rooms at around 24°C (75°F). For consistency, measure in a comfortably warm room.
Arousal level also plays a role. A partial erection will give you a shorter reading than your actual maximum. If you’re not fully erect, the number won’t reflect your true size. Taking the measurement at peak firmness gives the most accurate result.
Body weight is the biggest source of discrepancy between individuals using the same technique. The fat pad over the pubic bone can hide a meaningful portion of the shaft. This is exactly why the bone-pressed method exists: it bypasses that variable. Two men with the same anatomical penile length but different body fat levels will get different non-bone-pressed numbers but similar bone-pressed numbers.
Common Mistakes
- Measuring from the side or underside. The standard is along the top of the shaft. The underside includes extra length from the curvature toward the scrotum, which inflates the number.
- Using a flexible tape for length. A flexible tape follows any curve in the shaft, which adds length that a straight-line measurement wouldn’t capture. Use a rigid ruler for length and save the tape for girth.
- Not pressing to the bone. Skipping this step is fine if you just want a personal reference, but it makes comparison to study data unreliable, especially if you carry extra weight around the midsection.
- Measuring at inconsistent times. Erection quality varies with stress, fatigue, and time of day. If you’re measuring more than once for consistency, try to replicate similar conditions.
How Averages Are Reported
A 2023 meta-analysis in the World Journal of Men’s Health pooled data from 75 studies and over 55,000 men. The averages: flaccid length was 8.7 cm (about 3.4 inches), stretched flaccid length was 12.9 cm (5.1 inches), and erect length was 13.9 cm (5.5 inches). These are bone-pressed measurements. If you used the non-bone-pressed method, your number will naturally fall a bit below these figures, and that doesn’t mean you’re below average.
For clinical context, a micropenis is defined as a stretched length more than 2.5 standard deviations below the mean for age. In adults, that threshold falls well below the numbers most men will measure. The vast majority of men who feel concerned about their size fall within the normal statistical range.