To measure your penis properly, you need a ruler or measuring tape, a full erection, and a consistent technique called bone-pressed erect length. This is the same method urologists use in clinical studies, and it gives the most accurate, reproducible number. The process takes about a minute once you know what you’re doing.
What You Need
For length, a rigid ruler works well for a straight penis. If you have noticeable curvature, use a flexible measuring tape instead so you can follow the contour of the shaft. For girth (circumference), you’ll need a flexible measuring tape. If you don’t have one, wrap a piece of string around the shaft, mark where it overlaps, then measure the string against a ruler.
One thing to watch: some fabric measuring tapes stretch slightly when pulled taut, which can inflate your reading. Use light, consistent tension.
How to Measure Length
The standard clinical method measures along the top (dorsal) surface of the penis, from the pubic bone to the tip of the head. Here’s how to do it:
- Get fully erect. Partial erections give shorter, inconsistent readings.
- Stand upright and hold your penis straight out, perpendicular to your body.
- Press the ruler or tape firmly against your pubic bone at the base of the penis, right where the shaft meets your body on top. Push through any soft tissue until you feel bone.
- Read the measurement at the tip of the head (the glans).
This “bone-pressed” approach is important because it accounts for the fat pad above the penis. Everyone has some soft tissue there, and its thickness varies with body weight. Pressing to the bone gives a measurement that reflects your actual penile length rather than how much tissue happens to sit in front of it. In surgical cases involving a buried penis, the difference between a surface measurement and a bone-pressed one can be 2 cm or more.
If you don’t press to the bone, you’re measuring what’s sometimes called “non-bone-pressed” length. That number is fine for your own tracking, but it will be shorter, and it won’t match the method used in most size studies.
Measuring With Curvature
If your penis curves noticeably upward, downward, or to one side, a rigid ruler placed along the top won’t follow the actual length of the shaft. Lay a flexible tape along the top surface, following the curve from the pubic bone to the tip. This captures the true length rather than the straight-line distance between two points, which would undercount.
Curvature up to about 30 degrees is common and doesn’t require any special consideration beyond using a flexible tape. More pronounced bending, especially if it developed over time or comes with hard spots in the shaft, may be worth mentioning to a doctor, as that pattern is characteristic of Peyronie’s disease.
How to Measure Girth
Wrap a flexible measuring tape around the thickest part of the shaft while fully erect. For most people this is roughly mid-shaft, but it can be closer to the base or the head. Don’t compress the tissue. Just let the tape sit snugly against the skin and read where it overlaps.
If you’re measuring in multiple spots, note each location. The shaft isn’t perfectly uniform, so a single girth number is really just a representative measurement at one point.
Why Consistency Matters More Than a Single Number
Erection quality fluctuates with arousal level, temperature, time of day, stress, and blood flow. A measurement taken at peak arousal on a warm evening may differ from one taken when you’re slightly distracted on a cold morning. If you want a reliable number, measure on three or four separate occasions using the same technique, then take the average.
Room temperature matters more than you’d think. Cold causes the tissue to contract, which affects both flaccid and erect size. A neutral or warm environment gives the most consistent conditions.
The Stretched Flaccid Method
If you need an estimate without a full erection, the stretched flaccid length is a reasonable proxy. Retract the foreskin if applicable, grip the head between your thumb and forefinger, and gently extend the penis straight outward until it’s fully stretched but not uncomfortable. Measure from the pubic bone to the tip, just like the erect method.
Clinicians use this technique when an erection isn’t practical, such as during routine exams or pre-surgical assessments. It correlates well with erect length for most men, though it tends to run slightly shorter.
How Self-Measurements Compare to Clinical Data
Self-reported measurements tend to run significantly higher than those taken by clinicians. A study that sent participants a printed ruler (at true 1:1 scale, to prevent tampering) and instructions found that men’s self-reported erect length averaged 18.02 cm. That’s about 21% larger than the clinically measured average for the same population. By contrast, the same participants self-reported their height only about 1% above the national average, and their weight was statistically identical to it. Penis size was the one measurement with a dramatic gap between self-report and reality.
The most cited clinical dataset, a meta-analysis covering over 15,500 men measured by health professionals, puts the average erect length at 13.12 cm (about 5.2 inches) and the average erect circumference at 11.66 cm (about 4.6 inches). These numbers come from standardized bone-pressed measurements, so if you use the technique described above, your result is directly comparable.
Common Mistakes That Skew Results
Measuring along the underside of the penis instead of the top gives a longer number because the underside contour extends further back toward the scrotum. Clinical protocols specify the top (dorsal) surface for consistency. Measuring from the side introduces a similar problem.
Starting at the skin surface rather than pressing to the pubic bone will undercount, especially if you carry extra weight in the lower abdomen. Not being fully erect is probably the most common source of inconsistency: even a 10% drop in rigidity changes the reading noticeably.
Pressing a ruler into the skin at an angle rather than straight back toward the bone can also add a fraction of a centimeter that isn’t real. Keep the ruler perpendicular to your body and push straight back.