To measure penis size accurately, you need a rigid ruler for length and a flexible measuring tape for girth, and you should measure while fully erect. The standard clinical method, called bone-pressed erect length, gives you the most consistent and comparable result. Here’s exactly how to do both measurements and what the numbers mean.
How to Measure Length
Stand upright with a full erection. Place a rigid ruler on top of your penis, right where the shaft meets your body at the base. Press the end of the ruler firmly against the pubic bone, pushing past any fat or hair at the base. This is called the “bone-pressed” method, and it’s what doctors and researchers use because it eliminates variation caused by body fat. Without pressing to the bone, two people with identical actual length could get very different numbers depending on their weight.
From that pressed starting point, measure in a straight line along the top of the shaft to the very tip of the head. If your penis curves, don’t follow the curve with a flexible tape. Use the ruler to measure the straight-line distance, or if the curve is significant, a flexible tape held along the top surface will give a more functional measurement. Record the number in inches or centimeters.
Measuring Without an Erection
If measuring erect isn’t practical, you can use the stretched flaccid method. Gently stretch the penis outward from your body while flaccid and measure from the pubic bone to the tip, the same way described above. Research published in the Journal of Urology confirmed that stretched flaccid length closely correlates with erect length, making it a reliable substitute. Regular flaccid length (unstretched) is not a good predictor of erect size because flaccid measurements vary too much from moment to moment.
How to Measure Girth
Girth is the circumference, the distance around the shaft. You’ll need a soft, flexible measuring tape (the kind used for sewing). With a full erection, wrap the tape around the thickest part of the shaft, typically around the middle. Pull it snug but not tight enough to compress the skin. Where the tape meets its starting point is your girth measurement.
If you don’t have a measuring tape, wrap a strip of paper or a piece of string around the shaft, mark where it overlaps, then lay it flat against a ruler. Girth matters more than length for condom fit, so if you’re measuring to find the right condom size, this is the number to pay closest attention to.
What Counts as Average
A large meta-analysis published in BJU International compiled data from over 15,500 men and established reliable averages. The mean erect length was 13.12 cm (about 5.16 inches). The mean erect girth was 11.66 cm (about 4.59 inches). For context, flaccid length averaged 9.16 cm (3.6 inches), which illustrates why flaccid size tells you relatively little about erect size.
These numbers follow a normal distribution, meaning most men cluster near the average with fewer at either extreme. Roughly 68% of men fall within one standard deviation of the mean, which works out to an erect length between about 4.5 and 5.8 inches.
Factors That Affect Your Measurement
Don’t be surprised if you get slightly different numbers on different days. Several factors cause temporary variation:
- Temperature: Cold environments cause significant temporary shrinkage in flaccid size, and even erect measurements can vary slightly based on ambient temperature.
- Arousal level: A partial erection will give a shorter measurement than a full one. Make sure you’re at maximum firmness before measuring.
- Time of day: Testosterone levels and blood flow fluctuate throughout the day, which can influence erection quality.
- Body weight: The bone-pressed method controls for this, but if you’re measuring without pressing to the pubic bone, a larger fat pad at the base will hide more of the shaft and reduce your visible measurement.
For the most accurate result, measure on two or three separate occasions and average the numbers.
Common Measurement Mistakes
The most frequent error is not pressing the ruler to the pubic bone. The fat pad above the base of the penis can be over a centimeter thick, and skipping the bone press means you’re underestimating by that much. This is also why weight loss can make the penis appear longer without any actual change in size: the fat pad shrinks, revealing more of the shaft.
Measuring along the underside of the shaft instead of the top also introduces error, since the underside is typically longer due to how the penis attaches to the body. Always measure along the top (the dorsal surface). Similarly, measuring from the side rather than the top will skew your number. Consistency matters: same position, same method, same level of arousal.
Using Your Measurements for Condom Fit
Condom sizing is based primarily on girth, not length. Most standard condoms fit a girth of roughly 4.4 to 5.2 inches (11.2 to 13.2 cm). If your girth is below that range, look for snug or slim-fit options. Above that range, large or extra-large condoms will be more comfortable and less likely to break. A condom that’s too tight restricts blood flow and increases breakage risk, while one that’s too loose can slip off.
Length matters less because condoms don’t need to unroll completely to work. Most standard condoms are about 7.5 inches long, which accommodates the vast majority of men. If a condom is too long, simply don’t unroll it all the way.