To measure your penis accurately, you need a rigid ruler for length and a flexible measuring tape for girth. The standard method used in clinical research involves measuring along the top of the shaft while pressing the ruler against the pubic bone, which gives the most consistent and reproducible result.
How to Measure Length
Get fully erect first. Measurements taken while flaccid vary too much from one attempt to the next because blood flow, temperature, and arousal all change your resting size. An erect measurement is the only reliable one.
Place a rigid ruler along the top of your penis (the side facing your abdomen, not the underside). Position the end of the ruler where the shaft meets your body at the pubic bone. Press the ruler firmly into the pubic bone, pushing past any fat pad or pubic hair at the base. Read the measurement at the tip. This technique is called a bone-pressed erect length measurement, and it’s the standard used in virtually every clinical study on penis size. Pressing to the bone matters because the fat pad above the base can obscure a significant portion of the shaft, especially at higher body weights. This gives you your true structural length rather than just what’s visible.
If you want to know your visible length instead, simply place the ruler on top without pressing into the fat pad. The difference between the two numbers tells you how much length the fat pad is concealing.
How to Measure Girth
While fully erect, wrap a soft, flexible measuring tape around the thickest part of the shaft. For most people this is roughly at the midpoint, though some find the base or area just below the head is widest. Pull the tape snug against the skin without compressing the tissue, and read the circumference where the tape overlaps. If you don’t have a fabric measuring tape, wrap a strip of paper or string around the shaft, mark where it overlaps, then lay it flat against a ruler.
How Your Numbers Compare
A large meta-analysis published in BJU International combined data from over 15,000 men measured by health professionals across multiple countries. The averages were:
- Erect length: 13.12 cm (5.16 inches)
- Erect circumference: 11.66 cm (4.59 inches)
- Flaccid length: 9.16 cm (3.61 inches)
These are means, so roughly half of all men fall below these numbers and half above. The distribution is a bell curve, meaning most men cluster fairly close to the average and very few are at either extreme. Flaccid size is also a poor predictor of erect size. Some men grow substantially when aroused while others show relatively little change.
Why Consistent Technique Matters
Small changes in method can shift your result by half an inch or more. Measuring along the underside of the shaft gives a longer number because of the curve most penises have. Measuring from the side introduces the width of the shaft into the starting point. Neither of these matches how clinical studies collect data, so your result won’t be comparable to published averages.
Erection quality also matters. If you’re 80% erect versus fully erect, you’ll get a shorter and thinner reading. Arousal level, time of day, room temperature, and even stress can all influence how firm your erection is on a given attempt. If you want a reliable number, measure on a few separate occasions when fully aroused and take the average.
Using Your Measurements for Condom Fit
Girth is the more important measurement for condom sizing. A condom that’s too tight is uncomfortable and more likely to break. One that’s too loose can slip off. Standard condoms are designed for a girth roughly between 4 and 5 inches (10 to 12.7 cm) and a length between 5 and 7 inches. If your girth is below that range, look for snug or slim fit options. If you’re above it, large or XL sizes use a wider lay-flat width that accommodates thicker shafts without constricting blood flow.
Condom brands list a “nominal width” on the packaging, which is the lay-flat width of the condom (half the circumference of the opening). Dividing your girth measurement by two gives you a rough starting point for finding the right nominal width, though most people find the right fit through a little trial and error.
When Size May Be a Medical Concern
A clinical micropenis is defined as a stretched or erect length more than 2.5 standard deviations below the mean. In practical terms, that translates to a stretched length of about 2.67 inches (6.8 cm) or less in an adult. This is a recognized medical condition, not just being on the smaller side of normal, and it’s quite rare. It’s typically caused by hormonal factors during fetal development. If your measurements fall in this range, a urologist can evaluate whether any underlying hormonal issue is involved and discuss options if the size causes functional difficulty.
For everyone else, variation within the normal range is just that: normal. The bell curve is tighter than most people assume, and the gap between the 25th and 75th percentile is only about an inch in length.