The standard way to measure penile length is with a rigid ruler pressed against the pubic bone at the top of the shaft, measuring to the tip of the glans. This method, called bone-pressed erect length, is what clinical studies use and gives you the most consistent, comparable number. Getting an accurate measurement takes a bit more than just holding a ruler up, though, so here’s how to do it right.
How to Measure Length
You need a full erection and a rigid ruler (not a flexible tape). Place the ruler along the top of the penis, pressing the end firmly into the pubic bone where the shaft meets your body. This compresses the fat pad above the base, which can otherwise hide a significant portion of actual length. Read the measurement at the very tip of the glans.
Measuring from the top (the side facing your stomach) is the standard position. Measuring from the bottom or sides will give you a different, less standardized number because of the way the shaft attaches to the body. Keep the ruler straight and parallel to the shaft. If you’re not fully erect, the number will be shorter than your true measurement, so consistency matters.
If you want to measure without an erection, stretched flaccid length is a reliable stand-in. Research confirms that stretched length closely correlates with erect length. To do this, hold the head of the penis and stretch it outward (gently, not painfully) while pressing the ruler against the pubic bone. This is the method urologists most commonly use in clinical settings because it doesn’t require an erection.
How to Measure Girth
Girth is the circumference of the shaft, and for this you do need a flexible measuring tape, sometimes called a tailor’s tape. Wrap it snugly around the shaft without compressing the tissue, then read the number where the tape overlaps.
The most common location to measure is the mid-shaft, roughly halfway between the base and the glans. Some people measure at the base or just behind the head (the corona) as well, since girth can vary along the length. If your shaft is noticeably thicker in one area, measuring at multiple points gives you a more complete picture. Just be clear with yourself about where you measured so you can compare consistently over time.
Dealing With Curvature
If your penis curves noticeably upward, downward, or to one side, a rigid ruler will underestimate your length because it measures in a straight line while your anatomy follows a curve. For a curved shaft, a flexible tape laid along the longer (outer) side of the curve from the pubic bone to the tip captures the full length of tissue. This gives you the most accurate reading of actual size.
For men with Peyronie’s disease, where a plaque causes a more pronounced bend, urologists recommend documenting both the stretched length (from the skin junction at the base to the tip) and the point of maximum curvature. If you’re tracking changes related to a condition, measuring in the same way each time matters more than the specific method you choose.
Common Mistakes That Skew Results
Measuring from the side or underside of the shaft instead of the top is the most frequent error. The top surface, pressed to the pubic bone, is the standardized approach used in virtually all research. Measuring from elsewhere typically adds length because of the angle and the way the shaft extends internally.
Using a flexible tape for length (rather than girth) can also introduce error. A soft tape tends to follow every surface contour and irregularity of the skin, which can add small amounts of length that a straight rigid ruler wouldn’t. Save the flexible tape for circumference.
Temperature and arousal level both affect size, especially flaccid size. Cold environments cause significant shrinkage that has nothing to do with your actual dimensions. If you’re measuring flaccid for any reason, a warm room and relaxed state will give you a more representative number. For erect measurements, make sure you’re at full erection, not partial.
How Your Numbers Compare
A large systematic review published in BJU International, covering over 15,000 men, established 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)
- Flaccid girth: 9.31 cm (3.66 inches)
Notice that stretched flaccid length (13.24 cm) and erect length (13.12 cm) are nearly identical in this dataset, which reinforces why the stretched method works as a proxy. These numbers represent the middle of the bell curve. Most men fall within about 1.5 to 2 cm of the mean in either direction. The standard deviation for erect length was 1.66 cm, meaning roughly two-thirds of men measured between about 11.5 and 14.8 cm (4.5 to 5.8 inches).
Bone-Pressed vs. Non-Bone-Pressed
You’ll sometimes see these abbreviated as BP (bone-pressed) and NBP (non-bone-pressed). The difference is simply whether you push the ruler into the fat pad above the pubic bone. Non-bone-pressed gives you the visible length, which is what a partner would see. Bone-pressed gives you the total anatomical length, which is more consistent and comparable because it removes the variable of body fat.
The gap between the two depends entirely on how much fat sits over your pubic bone. For a lean person, the difference might be a quarter inch. For someone carrying more weight, it could be an inch or more. Neither number is “wrong,” but if you’re comparing to published averages, those studies almost always use bone-pressed measurements.