To measure a penis accurately, you need a ruler or flexible measuring tape, a full erection, and a consistent technique called the “bone-pressed” method. This is the same approach used in clinical studies, and it gives you the most reliable, repeatable number. The whole process takes about a minute once you know what you’re doing.
How to Measure Length
Stand upright with a full erection. Place a rigid ruler or measuring tape along the top (dorsal) side of the penis, which is the side facing up when the penis points straight out from your body. Press the end of the ruler firmly against the pubic bone, pushing it into the fat pad at the base. This is the “bone-pressed” method, and it matters because the soft tissue covering the pubic bone can hide anywhere from a fraction of an inch to over an inch of actual length, depending on your body composition. Measure in a straight line from the pubic bone to the very tip of the glans.
If your penis has a noticeable curve, use a flexible measuring tape instead of a rigid ruler. Lay the tape along the top surface, following the curve, so you capture the full length rather than cutting across it in a straight line. European Association of Urology guidelines consider this dorsal measurement from the pubic bone to the tip of the glans the standard for penile length.
One alternative you may see referenced is a “skin-to-tip” measurement, where you start at the skin surface rather than pressing to the bone. This method is simpler but less consistent because results shift with weight changes. The bone-pressed technique eliminates that variable, which is why researchers and urologists prefer it.
How to Measure Girth
Girth is the circumference of the shaft. With a full erection, wrap a flexible measuring tape around the thickest part of the shaft. For most people, this is at mid-shaft, but it can vary. Note where the tape meets itself without overlapping or pulling tight. That number is your girth.
If you don’t have a flexible tape, wrap a piece of non-stretchy string around the shaft, mark where it overlaps with a pen or pinch it between your fingers, then lay the string flat against a ruler. Clinical guidelines from the EAU recommend recording girth at both mid-shaft and just behind the head (the coronal area) for a complete picture, but for personal measurement, the thickest point is the most useful single number.
Getting Consistent Results
Penis size fluctuates throughout the day based on temperature, blood flow, hydration, and arousal level. A cold room can noticeably reduce size, both flaccid and erect. For the most accurate measurement, make sure you’re fully erect, warm, and in a comfortable setting. If you’re comparing measurements over time, try to replicate similar conditions each time.
A few common mistakes to avoid:
- Measuring from the side or underside. Always measure along the top (dorsal) surface. The underside includes the frenulum and tends to give a shorter reading, while side measurements are inconsistent.
- Skipping the bone press. Without pressing to the pubic bone, your result depends on how much fat tissue sits at the base. This is the single biggest source of inaccuracy in self-measurement.
- Using a stretchy tape. Some fabric measuring tapes have give to them. Pull gently and consistently. If the tape stretches, you’ll get an inflated number.
- Measuring without a full erection. Partial erections undercount length and girth significantly. If you lose your erection mid-measurement, wait and try again.
What If You Can’t Measure Erect?
Clinicians often use stretched flaccid length as a stand-in for erect length because it’s easier to measure in a medical setting. To do this, hold the penis by the glans and stretch it outward, parallel to the floor, without causing discomfort. Measure from the pubic bone to the tip of the glans while stretched. Research published in The Journal of Urology found that stretched flaccid length predicts erect length with roughly 79% accuracy, making it a reasonable approximation when an erect measurement isn’t practical.
How Your Numbers Compare
A large meta-analysis published in BJU International compiled data from over 15,500 men measured by healthcare professionals using standardized methods. The averages were:
- Erect length: 13.12 cm (about 5.16 inches)
- Erect circumference: 11.66 cm (about 4.59 inches)
- Flaccid length: 9.16 cm (about 3.61 inches)
- Stretched flaccid length: 13.24 cm (about 5.21 inches)
These numbers represent the midpoint of a normal distribution, meaning most men cluster around these values with relatively small variation in either direction. Flaccid size is a poor predictor of erect size. Some men who appear smaller when flaccid gain proportionally more length during erection, and vice versa. This is normal variation in how much blood the erectile tissue holds relative to its resting state.
Why Measurement Method Matters
The reason clinicians and researchers are so specific about technique is that small changes in method produce meaningfully different numbers. Measuring from the side instead of the top, starting at the skin surface instead of the bone, or measuring at partial erection can each reduce or increase the result by half an inch or more. If you’re measuring for condom sizing, tracking changes after weight loss, or simply satisfying curiosity, the bone-pressed erect method on the dorsal surface gives you the most accurate and comparable number. It’s the closest thing to a universal standard, and it’s the method behind virtually every clinical dataset on penis size.