The most accurate way to measure your penis is along the top of the shaft, from the pubic bone to the tip of the head, using what’s known as the “bone-pressed” method. This is the standard technique used in medical research and gives the most consistent, reproducible result regardless of body weight. Here’s exactly how to do it for both length and girth.
Measuring Length
You’ll need a rigid ruler rather than a flexible tape measure for length. Stand upright and place the ruler on top of your penis (the side facing your abdomen, not the underside). Position the end of the ruler at the base where the shaft meets the pubic bone, then press it firmly into the bone, pushing past any fat pad or pubic hair. Measure in a straight line to the very tip of the head.
Pressing into the pubic bone matters because the layer of fat in that area varies from person to person, and it changes with weight gain or loss. Without pressing in, two people with identical anatomy could get different numbers simply because one carries more fat in that area. The bone-pressed technique removes that variable, which is why researchers consider it more accurate and reliable, with the biggest discrepancies showing up in overweight individuals.
If the shaft has a curve, keep the ruler along the top surface and measure the straight-line distance. Don’t trace the curve with a tape measure for length, as that inflates the number and doesn’t match how size is reported in studies.
Erect vs. Flaccid: Which to Measure
Erect length is the standard measurement in most research. Flaccid length is a poor predictor of erect size because penises vary dramatically in how much they grow during arousal. Research published in The Journal of Urology found that flaccid length only accounts for about 68% of the variation in erect length, meaning it’s not reliable on its own.
If measuring while erect isn’t practical, there’s a good alternative: stretched flaccid length. Grip the head gently and extend the penis to its maximum stretch without causing discomfort, then measure the same way (bone-pressed, along the top, to the tip). Stretched flaccid length predicts erect length much more closely, accounting for about 79% of the variation. Urologists regularly use this method when counseling patients, and it’s considered a suitable estimate.
Measuring Girth
For circumference, use a flexible fabric tape measure or a thin strip of paper you can mark and then hold against a ruler. Wrap it snugly around the shaft at its widest point, which for most men is somewhere around the mid-shaft. Don’t pull the tape tight enough to compress the tissue, just snug against the skin.
Girth should be measured while erect, since circumference changes significantly with arousal. If the shaft varies noticeably in thickness along its length, you can take measurements at the base, mid-shaft, and just below the head, then note the largest.
Getting a Consistent Result
Several factors can throw off your measurement if you’re not aware of them. Cold temperatures cause vasoconstriction, temporarily reducing size. Anxiety triggers adrenaline, which does the same thing. Recent ejaculation and your level of arousal both affect how firm and full the erection is. For the most accurate reading, measure in a comfortable, warm room when you’re fully aroused and relaxed.
It’s worth measuring a few times on different days rather than relying on a single attempt. Small variations between sessions are normal. If you get a range, the middle of that range is your most reliable number.
Bone-Pressed vs. Non-Bone-Pressed
You may see the terms “bone-pressed” (BP) and “non-bone-pressed” (NBP) in online discussions. The difference is straightforward: bone-pressed means you push the ruler into the pubic bone, and non-bone-pressed means you rest it lightly on the skin surface without pressing in. The non-bone-pressed method captures only the “usable” length that extends visibly from the body, so it produces a shorter number, sometimes by half an inch or more depending on how much fat sits over the pubic bone.
Neither method is wrong, but they measure slightly different things. Medical studies almost universally use bone-pressed because it’s more consistent across different body types and doesn’t fluctuate with weight changes. If you’re comparing yourself to published averages, use bone-pressed to get an apples-to-apples comparison.
How Your Measurement Compares
A widely cited review of over 15,000 men found the following averages:
- Erect length: 5.1 inches (13.0 cm)
- Erect girth: 4.5 inches (11.5 cm)
- Flaccid length: 3.6 inches (9.1 cm)
- Flaccid girth: 3.7 inches (9.3 cm)
These numbers represent the middle of the bell curve. Most men fall within roughly an inch above or below the average for both length and girth. If you’re anywhere in that range, you’re statistically typical. Keep in mind that self-reported surveys tend to run higher than studies where a clinician does the measuring, so be cautious about comparisons you find in informal online polls.