To measure penis length accurately, you place a ruler or measuring tape along the top of the shaft, from the base where the penis meets the body to the tip of the head. For the most consistent and comparable result, you press the ruler firmly against the pubic bone, compressing any fat pad at the base. This “bone-pressed” method is the standard used in medical studies and urology clinics because it gives a true maximum length regardless of body weight.
Step-by-Step Length Measurement
You’ll need a rigid ruler or a non-stretchy measuring tape and a full erection. Stand or sit in a comfortable position, then place the ruler along the top (dorsal) surface of the penis. The starting point is the spot where the shaft meets the pubic area, and the endpoint is the very tip of the head. Press the end of the ruler straight back into the pubic bone so it compresses the skin and any fat underneath. Read the measurement at the tip.
If you only have a flexible measuring tape, be careful not to pull it taut enough to stretch it, since some tapes are elastic and will add length that isn’t there. A piece of string held against a rigid ruler afterward works as a backup. Measure two or three times on different occasions and average the results, since erection firmness can vary with arousal level, time of day, and temperature.
Bone-Pressed vs. Non-Bone-Pressed
You’ll sometimes see these referred to as BPEL (bone-pressed erect length) and NBPEL (non-bone-pressed erect length). The difference is simple: bone-pressed means you push the ruler into the fat pad until it stops against the pubic bone. Non-bone-pressed means you rest the ruler where the skin meets the shaft without pressing in at all.
Bone-pressed is the measurement used in virtually all clinical studies, and it’s the one you should use if you’re comparing yourself to published averages. The reason is consistency. Non-bone-pressed length changes depending on how much fat sits above the pubic bone, so two people with identical actual penile tissue could get very different readings. Think of it like measuring your height while standing fully upright rather than slouching. Bone-pressing isn’t about inflating numbers; it’s about having a reliable baseline.
That said, non-bone-pressed length tells you something useful too: it’s the visible length during sex. If losing weight is relevant to you, the gap between your bone-pressed and non-bone-pressed measurements reflects the thickness of your pubic fat pad, and that gap shrinks as body fat decreases.
Common Mistakes to Avoid
Measuring from the side or the underside of the shaft is the most frequent error. The underside includes extra tissue along the urethra and curves differently, so it almost always gives a longer, inaccurate number. Always measure along the top surface.
Other common pitfalls:
- Measuring when not fully erect. A partial erection can undercount by a centimeter or more. Wait until you’re at maximum firmness.
- Starting from the wrong spot. The ruler should contact the body where the top of the shaft begins, not further down near the scrotum.
- Curving with the tape. If your penis has a noticeable curve, hold the ruler straight and measure the chord (straight-line distance) rather than following the curve with a flexible tape. Some researchers do measure along the curve, but straight-line is more standard for length comparisons.
- Using a stretchy measuring tape pulled tight. This can add several millimeters you don’t actually have.
How to Measure Girth
Girth is the circumference around the thickest part of the shaft. Wrap a flexible measuring tape (or a strip of paper or string) around the widest point, mark where it overlaps, and measure the distance with a ruler. Do this while fully erect. If the shaft varies noticeably in thickness along its length, the midshaft point is the most commonly used location in studies.
Stretched Flaccid Length and Why Clinicians Use It
Doctors often skip the erect measurement entirely during an office visit, for obvious practical reasons. Instead, they measure stretched flaccid length: the penis is gently pulled straight out from the body while flaccid, and the distance from the pubic bone to the tip is recorded. Research published in The Journal of Urology found that stretched flaccid length correlates closely with erect length (R² = 0.79), making it a reliable stand-in. Unstretched flaccid length, by contrast, is a poor predictor of erect size because flaccid length varies enormously with temperature, blood flow, and stress.
How Your Numbers Compare
The largest systematic review of penile measurements, covering over 15,500 men, found the following averages (all bone-pressed):
- Erect length: 13.12 cm (5.16 inches), with a standard deviation of 1.66 cm
- 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)
A standard deviation of 1.66 cm means roughly 68% of men fall between about 4.5 and 5.8 inches erect. If you’re anywhere in that range, you’re squarely in the middle of the distribution. Flaccid size tells you very little about erect size; some men grow significantly more than others during erection.
When Size Falls Outside the Normal Range
Micropenis is a formal medical diagnosis, not just a casual term. It applies when stretched penile length falls more than 2.5 standard deviations below the average. For adults, that threshold is about 3.67 inches (9.3 cm) stretched. For newborns, the cutoff is 0.75 inches (1.9 cm). The condition is typically identified at birth and is linked to hormonal factors during fetal development. It’s rare, affecting well under 1% of the population.
Body Weight and Visible Length
The pubic fat pad can hide a significant portion of penile length. Research measuring both bone-pressed and non-bone-pressed dimensions found that the difference between the two directly reflects the thickness of that fat pad. In men carrying substantial weight in the lower abdomen, the buried portion can be an inch or more. The underlying penile tissue doesn’t shrink with weight gain, but the visible, functional length does decrease. Weight loss is the most straightforward way to recover that hidden length without any medical intervention.