To measure your penis accurately, you need a rigid ruler or measuring tape, a full or near-full erection, and a consistent technique. The standard method used in clinical research is called “bone-pressed” measurement, where you press the ruler against the pubic bone to account for the fat pad that sits above the base of the shaft. Here’s exactly how to do it for both length and girth.
How to Measure Length
Stand upright or stand at a slight angle where you can see comfortably. With a full erection, place a rigid ruler or straight measuring tape along the top of your penis, starting where the shaft meets your body. Press the end of the ruler firmly into the pubic bone, pushing past any fat or pubic hair. Then measure in a straight line from that point to the very tip of the head (glans).
A few details matter here. Always measure from the top, not the side or underside, since the underside includes extra tissue that inflates the number. If your penis has a curve, you can use a flexible tailor’s tape pressed gently along the top surface to follow the curve, though a rigid ruler in a straight line is the clinical standard. The bone-pressed technique is important because the pubic fat pad can bury anywhere from half an inch to two inches of the shaft, depending on body weight. Pressing to the bone gives you a consistent baseline regardless of weight fluctuations.
How to Measure Girth
Girth is the circumference of the shaft. Use a flexible measuring tape or a strip of string you can mark and then lay flat against a ruler. With a full erection, wrap the tape around the thickest part of the shaft, which for most people is roughly mid-shaft. Pull the tape snug but not tight enough to compress the tissue. Read the measurement where the tape overlaps.
If the head is noticeably thicker or thinner than the shaft, you may want to measure both the mid-shaft and base to get a complete picture, especially if you’re sizing for condoms.
Getting a Consistent Result
Penis size varies throughout the day based on several factors. Temperature, arousal level, time since last ejaculation, and even stress all influence erect size. Cold environments cause significant shrinkage in flaccid length and can reduce erect fullness. For the most reliable number, measure on multiple occasions (three or more times across different days) and average the results. Try to measure at a similar arousal level each time, ideally at full erection.
Flaccid measurements are especially unreliable. Research from a multicenter study found that flaccid length was only moderately accurate at predicting erect length, and different observers measuring the same person often got different results. Erect measurements are far more consistent and more useful for practical purposes like condom fitting.
How Your Measurements Compare
The largest meta-analysis on penis size, published in BJU International and drawing from over 15,000 men, found these averages:
- Erect length: 13.12 cm (5.16 inches)
- Erect girth: 11.66 cm (4.59 inches)
- Flaccid length: 9.16 cm (3.61 inches)
- Stretched flaccid length: 13.24 cm (5.21 inches)
These are means with a standard deviation of roughly 1.5 to 1.9 cm for length and about 1 cm for girth. That means most men fall within about an inch above or below these averages. Stretched flaccid length closely approximates erect length for most people, which is why doctors sometimes use it as a proxy during physical exams.
Why Body Weight Affects Your Measurement
The pubic fat pad thickens with weight gain and buries part of the shaft beneath the skin’s surface. This doesn’t change your actual penile length, but it changes the visible and functional length. Men who carry significant weight in the lower abdomen can obscure a substantial amount of the shaft. Weight loss can reveal roughly 0.5 to 2 inches of previously hidden length, proportional to how much fat was there to begin with. This is one reason the bone-pressed method exists: it measures the full anatomical length regardless of body composition.
Using Your Measurements for Condom Sizing
Condom fit depends primarily on girth, not length. Manufacturers size condoms by “nominal width,” which is the diameter of the opening laid flat. To find your nominal width, divide your girth by 3.14. So if your girth is 5 inches, your nominal width is about 1.59 inches (roughly 40 mm).
Most U.S. manufacturers use these approximate ranges:
- Small/Snug: 49 to 52 mm nominal width
- Regular/Standard: 52 to 56 mm nominal width
- Large: 56 to 60 mm nominal width
- Extra-Large: 60 to 64 mm nominal width
A condom that’s too tight is more likely to break and less comfortable. One that’s too loose can slip off. Getting the right fit based on actual girth measurement is one of the most practical reasons to measure in the first place. Length matters less because most condoms don’t need to unroll completely to work properly.