To measure your penis size accurately, you need a ruler or flexible measuring tape, a full erection, and a consistent technique. The method used in most clinical research is called “bone-pressed” length, measured from the pubic bone to the tip of the glans. Here’s how to do it right, what the numbers mean, and how your results compare to published averages.
How to Measure Length
Stand upright with a full erection. Place a rigid ruler or measuring tape along the top of the penis (the side facing your abdomen, not the underside). Press the end of the ruler firmly against the pubic bone, pushing into the fat pad above the base of the penis. Read the measurement at the very tip of the glans.
This “bone-pressed” technique is the standard in medical research because it accounts for the layer of fat that sits over the pubic bone. Without pressing in, that fat pad shortens the reading, sometimes significantly. A systematic review in The Journal of Sexual Medicine found that measuring from the pubic bone to the tip of the glans is more accurate and reliable, and that the gap between bone-pressed and non-pressed measurements is most noticeable in men who carry extra weight. If you want a number you can meaningfully compare to published data, bone-pressed is the way to go.
If your penis has a noticeable curve, use a flexible measuring tape rather than a rigid ruler. Lay the tape along the curve on the top side, following the contour from the pubic bone to the tip. A rigid ruler will underestimate the length of a curved penis because it measures a straight line rather than the actual surface.
How to Measure Girth
Girth is circumference, the distance around the shaft. You need a flexible measuring tape for this. If you don’t have one, a piece of non-stretchy string works: wrap it around the shaft, mark where it meets itself, then measure that length against a ruler.
Wrap the tape around the thickest part of the shaft while fully erect. Pull it snug but not tight. Be cautious with fabric measuring tapes, as some have enough stretch to give an inflated reading. The thickest point is typically mid-shaft, though it varies from person to person. One consistent location is what matters most if you’re tracking over time.
Getting a Consistent Reading
Several factors can change your measurement from one attempt to the next, so controlling for them gives you a more reliable number.
- Arousal level: You need a full, firm erection. Partial erections will give a shorter and thinner reading. Blood flow to the penis increases tissue temperature by nearly 2°C during full arousal, which reflects the degree of engorgement. If you’re not fully aroused, the measurement won’t represent your actual size.
- Room temperature: Cold causes the penis to retract. Measure in a comfortably warm room, not after stepping out of a cold shower or sitting in an air-conditioned space for a long time.
- Time of day: Testosterone peaks in the morning, and many men find erections are firmest then. Picking a consistent time reduces variability.
- Repeat measurements: Take two or three measurements on different days and average them. A single reading is a snapshot, not a reliable baseline.
Stretched Length as an Alternative
If measuring during an erection isn’t practical, stretched flaccid length is a reasonable substitute. Grip the glans gently, pull the penis straight out to its full stretch (without pain), and measure from the pubic bone to the tip using the same bone-pressed technique.
In clinical studies, about 60% of penile measurements are taken in the stretched state. It correlates with erect length, though not perfectly. A large multicenter study found that flaccid measurements were only “moderately accurate” at predicting erect length, and observer technique introduced variability. Stretched length tends to slightly overestimate or underestimate erect length depending on individual anatomy, so treat it as a close approximation rather than a precise equivalent.
How Your Measurements Compare
The largest meta-analysis on the topic, published in BJU International and covering over 15,500 men, established the following averages:
- Erect length: 13.12 cm (5.16 inches), with a standard deviation of 1.66 cm
- Erect circumference: 11.66 cm (4.59 inches), with a standard deviation of 1.10 cm
- Flaccid length: 9.16 cm (3.61 inches)
- Stretched length: 13.24 cm (5.21 inches)
Standard deviation tells you how spread out the data is. For erect length, roughly 68% of men fall between 11.46 cm (4.5 inches) and 14.78 cm (5.8 inches). If you’re within that range, you’re statistically in the middle of the distribution. Being outside it in either direction is also normal; it simply means you’re further from the center of the bell curve.
Notice that stretched flaccid length (13.24 cm) and erect length (13.12 cm) are very close on average, which is why the stretched method works as a proxy. Flaccid length on its own is a poor predictor of erect size. Some men show substantial growth from flaccid to erect, while others show very little, and neither pattern is unusual.
Why Measurement Method Matters
Most of the confusion around penis size comes from inconsistent technique. Measuring from the underside of the shaft adds length because the distance from base to tip is longer on the bottom. Not pressing to the pubic bone subtracts length, especially if you carry weight in your lower abdomen. Measuring at partial erection underestimates both length and girth.
If you’re measuring because you need a specific condom size, girth is actually the more important number. Condom fit depends on circumference, not length. Most condom sizing charts use girth measurements to recommend nominal width, so an accurate circumference reading at the thickest point of the shaft will help you find a better fit than eyeballing it off the shelf.