To measure penis length, place a ruler or measuring tape along the top of the penis, pressing gently into the pubic bone at the base, and measure to the tip of the head. This “dorsal” method, measuring along the top surface from base to tip, is the same technique used in clinical research and gives the most consistent, accurate result.
What You Need
A soft, flexible measuring tape is the best tool. It conforms to any natural curvature, which means you get an accurate reading even if your penis curves upward, downward, or to one side. A rigid ruler works fine for a straight penis, but it can underestimate length if there’s any bend. If you don’t have a measuring tape, wrap a piece of string along the length, mark it, and then hold it against a ruler.
Measuring Length Step by Step
Stand upright. Place one end of the tape or ruler at the point where the top of your penis meets your lower abdomen, pressing lightly into the pubic bone so that any fat pad over the bone doesn’t shorten your measurement. Run the tape along the top (dorsal) surface of the shaft in a straight line, or along the curve if your penis curves, all the way to the tip of the head. Read the measurement at the very tip.
Measure while fully erect for the most meaningful number. Flaccid size varies a lot depending on temperature, stress, arousal level, and even time of day. The penis is a dynamic organ that shifts between flaccid, semi-erect, and fully rigid states, and environmental factors like a cold room or feeling anxious can temporarily reduce flaccid size. An erect measurement eliminates most of that variability.
If measuring while erect isn’t practical, you can use the stretched flaccid method: gently stretch the flaccid penis to its full extent and measure the same way, from the pubic bone along the top to the tip. Clinical research treats stretched flaccid length as a reliable stand-in for erect length, with meta-analyses showing the two measurements produce nearly identical results. It’s not a perfect substitute, but it’s close enough that urologists use it routinely.
Measuring Girth
Wrap a flexible tape measure around the thickest part of the shaft, typically the middle, while erect. If you only have string, wrap it snugly (without squeezing), mark where it overlaps, then lay it flat against a ruler. Girth is the circumference of the shaft, not the diameter.
Common Mistakes That Skew Results
Measuring from the side or underside of the penis will give a different number than measuring along the top. The dorsal (top) surface is the clinical standard, so use that if you want a result you can compare to published data. Pressing too hard into the pubic bone inflates the number, while not pressing at all can underestimate it, especially if you carry extra weight in that area. A light, firm press is the goal.
Taking the measurement before you’re fully erect is another common source of error. Partial erections can be noticeably shorter than full ones. If your erection firmness fluctuates, measure a few times on different days and take the average.
How Your Measurement Compares
A large meta-analysis published in the World Journal of Men’s Health pooled data from 75 studies and more than 55,000 men worldwide. The averages: flaccid length was about 8.7 cm (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 measured using the same dorsal technique described above.
Averages vary somewhat by study population and measurement method, so treat these as a broad reference point rather than a precise cutoff. Most men fall within a range, and the distribution is roughly bell-shaped, meaning the vast majority cluster within a centimeter or two of the average in either direction.
Why Consistent Technique Matters
If you’re measuring for a practical reason, like finding the right condom size, the technique matters more than the exact number. Condom fit depends primarily on girth rather than length, so an accurate circumference measurement is especially useful. For length, consistency is key: use the same method, the same starting point at the pubic bone, and the same level of erection each time. That way, any comparison you make, whether to sizing charts or to a previous measurement, is based on the same baseline.