The clinical standard for measuring penis length is called the bone-pressed method: place a rigid ruler along the top of the penis, press it firmly against the pubic bone, and read the measurement at the tip. This technique accounts for the layer of fat above the pubic bone, which can hide 1 to 3 cm (roughly half an inch to over an inch) of actual length depending on body composition. Below is a complete guide to getting accurate, repeatable measurements for both length and girth.
Why the Bone-Pressed Method Matters
The fat pad sitting over your pubic bone varies in thickness from person to person and even changes on the same person with weight fluctuations. Two men with identical shaft lengths can get noticeably different readings if they simply measure from the skin surface, because one may have a thicker fat pad than the other. Pressing the ruler to the bone eliminates that variable entirely, which is why researchers and urologists use this approach in clinical studies. When you see published average sizes, those numbers almost always come from bone-pressed measurements.
If you measure without pressing to the bone (sometimes called “non-bone-pressed”), you’ll get a shorter number that reflects your visible length but isn’t comparable to clinical data. Either method is fine as long as you know which one you’re using and stay consistent.
How to Measure Erect Length
You need a rigid ruler, not a flexible tape measure. Flexible tape can follow curves and contours, which introduces error for a length measurement. Stand upright or stand at a slight angle that lets you see the ruler clearly. With a full erection:
- Position the ruler. Place it along the top surface of the penis (the side facing your abdomen when erect), not the underside or either side.
- Press to the pubic bone. Push the end of the ruler straight back into the fat pad until it contacts the bone beneath. This should feel firm but shouldn’t be painful.
- Read at the tip. Note the measurement at the very end of the glans (the head of the penis). Don’t include foreskin if it extends past the tip.
The top surface is used because it gives the most consistent landmark. The underside includes the urethra and varies more between individuals.
If You Have a Curved Erection
A noticeable curve, whether upward, downward, or to one side, can make a rigid ruler less accurate. In this case, use a flexible measuring tape or a piece of string placed along the top surface, following the curve from the pubic bone to the tip. If you use string, mark where the tip falls, then lay the string flat against a ruler to get your number.
How to Measure Girth
Girth (circumference) requires a flexible measuring tape or a piece of string. With a full erection, wrap the tape snugly around the thickest part of the shaft, which for most men is just below the head. Don’t pull the tape tight enough to compress the tissue, but don’t leave slack either. If you’re using string, pinch it where the ends meet and measure that length against a ruler.
Some penises are thickest at the base or mid-shaft rather than below the head. If your shape varies noticeably along the shaft, measure at the widest point for the most representative number.
What About Flaccid Measurements
Flaccid size is unreliable as a single measurement because it changes throughout the day. Temperature, stress, physical activity, and time of day all cause significant fluctuation. A cold room alone can temporarily reduce flaccid length considerably.
If you want a flaccid measurement that actually correlates with your erect size, use the stretched flaccid length method. Gently stretch the flaccid penis to its maximum extension, holding it by the head, and measure from the pubic bone to the tip using the same bone-pressed technique described above. Research published in The Journal of Urology found that stretched flaccid length predicts erect length with reasonable accuracy (R² of 0.79), while unstretched flaccid length is a much weaker predictor (R² of 0.68). This is the method urologists use when measuring in a clinical setting where an erection isn’t practical.
How Your Results Compare to Averages
A large meta-analysis covering over 15,500 men measured by healthcare professionals found the following averages:
- Erect length: 13.12 cm (5.16 inches)
- Erect circumference: 11.66 cm (4.59 inches)
- Flaccid length: 9.16 cm (3.61 inches)
- Stretched flaccid length: 13.24 cm (5.21 inches)
- Flaccid circumference: 9.31 cm (3.66 inches)
These are means, not ideals. The distribution follows a normal bell curve, meaning most men cluster fairly close to these numbers, with relatively few at either extreme.
Getting a Consistent, Repeatable Number
The most common source of measurement error isn’t the tool or technique. It’s arousal level. Erection firmness varies, and a partial erection will give you a shorter reading than a full one. For the most accurate result, measure at peak arousal. Taking two or three measurements on different days and averaging them will smooth out any day-to-day variation.
Body weight also plays a role. The fat pad above the pubic bone thickens with weight gain, which is why the bone-pressed method exists in the first place. In men carrying significant excess weight, the fat pad can effectively bury a portion of the shaft. The underlying penile length doesn’t change with weight gain, but the visible length does. Bone-pressed measurement captures the true shaft length regardless of body composition.
Measure at roughly the same time of day if you’re tracking changes over time. Room temperature should be comfortable, since cold causes smooth muscle contraction in the shaft that can reduce both length and girth even during erection.