Penis length is measured along the top of the shaft, from the base at the pubic bone to the tip of the head, using a rigid ruler or measuring tape. This “bone-pressed” method is the standard used in urology research because it accounts for differences in body fat and gives the most consistent, comparable result. Whether you’re measuring at home out of curiosity or tracking a change over time, the technique matters more than most people realize.
The Bone-Pressed Method
The standard clinical measurement is called bone-pressed erect length. You press the end of a rigid ruler firmly against the pubic bone at the base of the penis, on the top side (the side facing your abdomen), and measure straight out to the tip. Pressing into the pubic bone is the key step. It compresses the fat pad that sits above the base of the shaft, which can otherwise hide a significant portion of length, especially in men who carry extra weight around the midsection.
Measurements are taken along the dorsal surface, meaning the top of the penis as it faces away from your body. You don’t measure along the underside, and you don’t follow any curve. A straight line from the pubic bone to the tip of the glans is the standard. A rigid ruler tends to be more accurate than a flexible tape for length, since tape can follow contours and add small errors.
Erect vs. Stretched Flaccid Length
In clinical settings, doctors often measure stretched flaccid length rather than erect length. The technique is similar: the ruler is pressed against the pubic bone on the top side, and the penis is gently stretched to its full extent. The measurement runs from the pubic bone to the groove just behind the head of the penis (the coronal sulcus).
Stretched flaccid length is considered an excellent stand-in for erect length. A large meta-analysis published in BJU International, covering over 15,000 men, found that the average stretched flaccid length was 13.24 cm (5.21 inches), while the average erect length was 13.12 cm (5.16 inches). Those numbers are close enough that clinicians routinely use the stretched measurement when an erection isn’t practical to obtain in a medical office. For personal measurement, though, erect length is more straightforward.
How to Measure Girth
Girth is measured as the circumference of the shaft at its thickest point, typically just below the head. A flexible measuring tape works best. Wrap it snugly around the thickest part of the shaft without compressing the tissue. If you don’t have a measuring tape, wrap a piece of string around the shaft, pinch it where the ends meet, then lay the string flat against a ruler.
Why Body Fat Changes the Number
The fat pad above the base of the penis can bury a substantial portion of the shaft. This is the whole reason the bone-pressed technique exists. In men with significant weight around the midsection, the visible portion of the penis can be considerably shorter than the actual anatomical length. Cleveland Clinic describes “buried penis” as a condition where a normal-sized penis is hidden by surrounding fatty tissue and skin folds. Pressing the ruler to the pubic bone bypasses this variable and gives you the true structural length regardless of body composition.
If you’re comparing your measurement to published averages, make sure those averages also used the bone-pressed method. Most clinical studies do, but not all self-report surveys are consistent.
Self-Measurement vs. Clinical Results
Men who measure themselves tend to report longer numbers than what researchers find in controlled studies. In two well-known clinical studies where erections were induced under supervised conditions, the combined mean erect length was 5.3 inches (13.5 cm), with about 68% of men falling between 4.6 and 6.0 inches. Only about 2.5% measured over 6.9 inches, and 2.5% measured under 3.7 inches.
The gap between self-reported and clinician-measured data likely comes from inconsistent technique: not pressing firmly enough to the bone, measuring along the underside (which runs longer), rounding up, or measuring from a slightly different starting point. Using the same method every time eliminates most of these errors.
Measuring With Penile Curvature
If the penis has a noticeable curve, whether naturally or due to Peyronie’s disease, the standard approach is still a straight-line measurement along the top. You don’t follow the curve with a flexible tape, because that would overestimate functional length. The American Urological Association recommends measuring stretched length from the skin junction at the pubic bone to the tip or coronal sulcus in a straight line, which keeps the measurement consistent even when curvature is present.
Standing, Lying Down, or Sitting
Clinical measurements are typically taken while standing. Lying flat generally produces the same number, since the anatomy doesn’t change with position. Sitting can make it slightly harder to press the ruler firmly against the pubic bone because of the way abdominal tissue folds, so standing or lying flat tends to be more practical and repeatable.
Getting a Consistent Result
The biggest source of error in penis measurement is inconsistency between attempts. A few simple habits eliminate most variation:
- Use a rigid ruler for length and a flexible tape or string for girth.
- Always measure from the top (dorsal) surface, pressed to the pubic bone.
- Measure at full erection for the most reliable personal result.
- Take two or three measurements on different occasions and average them, since erection quality can vary day to day based on arousal, temperature, and blood flow.
Flaccid length is naturally variable. It changes with temperature, stress, and time of day, which is why it’s rarely used in research and isn’t a meaningful number to track. Erect or stretched flaccid measurements are far more stable and comparable.