To measure penis size accurately, you need a rigid ruler or flexible measuring tape, a full erection, and a consistent technique. The standard method used in medical studies involves measuring along the top of the shaft while pressing the ruler into the pubic bone. Here’s exactly how to do it for both length and girth.
How to Measure Length
Get a full erection first. Partial erections will give you a shorter, inconsistent reading every time. Once fully erect, place a rigid ruler or measuring tape along the top of your penis, starting where the shaft meets your body at the pubic bone. Press the end of the ruler firmly into the pubic bone, pushing past any excess fat or pubic hair. Then measure in a straight line from that point to the tip of the head.
Measuring from the top matters. The underside of the penis includes extra length from the scrotum attachment, which inflates the number and isn’t how clinical measurements are taken. Keeping the ruler parallel to the floor (if you’re standing) prevents angling tricks that add phantom length.
Bone-Pressed vs. Non-Bone-Pressed
You’ll sometimes see the terms BPEL and NBPEL. BPEL (bone-pressed erect length) means you push the ruler into the pubic bone before reading the measurement. NBPEL (non-bone-pressed erect length) means you place the ruler against the skin without pressing in at all.
The bone-pressed method is the medical standard. Nearly all published studies on penis size use it because it removes body fat as a variable. If you gain or lose 30 pounds, your NBPEL changes even though your actual penis hasn’t. Pressing to the bone gives you a consistent measurement regardless of weight fluctuations. That said, the non-bone-pressed number reflects what’s visually apparent, so both numbers have their uses.
How to Measure Girth
Girth is the circumference of the shaft. Use a flexible measuring tape or a strip of paper (you can mark the paper and then measure the marked length against a ruler). Wrap it around the thickest part of the shaft at full erection. Pull it snug but not tight enough to compress the tissue. Read the measurement where the tape meets itself.
If your penis varies noticeably in thickness along its length, you can measure at the base, the mid-shaft, and just below the head, then use the mid-shaft measurement as your standard. Most men find mid-shaft is the most representative number.
What Tools Work Best
A rigid ruler works well for length because it stays straight and presses easily against the pubic bone. A flexible tailor’s tape is better for girth since it wraps around curved surfaces. Using a rigid ruler for girth is difficult and inaccurate. If you only have a ruler, wrap a piece of string around the shaft, mark where it overlaps, then lay the string flat against the ruler.
Why the Fat Pad Matters
The pad of fat above the base of your penis directly affects how much length is visible. In men carrying significant extra weight, this fat pad can hide a substantial portion of the shaft. In severe cases, the penis can appear partially or fully buried beneath the tissue.
This is why the bone-pressed technique exists. It measures your full anatomical length regardless of body composition. Weight loss doesn’t actually increase penis size, but it does reduce the fat pad and reveal more usable length. If you’ve ever noticed your penis looks longer after losing weight, this is the reason.
Average Size for Reference
A large meta-analysis published in the World Journal of Men’s Health reviewed 75 studies covering over 55,000 men. The pooled averages were:
- Erect length: 13.93 cm (about 5.5 inches)
- Stretched flaccid length: 12.93 cm (about 5.1 inches)
- Flaccid length: 8.70 cm (about 3.4 inches)
These are bone-pressed measurements. If you measured without pressing, your number will typically be somewhat lower depending on your body composition. Flaccid size varies dramatically with temperature, stress, and activity level, so it’s a poor indicator of erect size.
When Size Falls Outside the Normal Range
Micropenis is a clinical diagnosis defined as a stretched length more than 2.5 standard deviations below the average for age. In adults, this translates to roughly 4 cm (about 1.6 inches) or less when stretched. This is rare and typically identified early in life. If your measurement falls within a few inches of the average in either direction, you’re within normal variation.
Tips for a Consistent Measurement
Measure at full erection. Even slight differences in arousal level change the result. Room temperature matters too, since cold environments reduce blood flow. Take a few measurements on different days and average them rather than relying on a single reading. Time of day, hydration, and how recently you’ve been physically active can all introduce minor variation.
Stretched flaccid length correlates reasonably well with erect length (research shows a correlation coefficient of about 0.73), but it’s a clinical shortcut, not a substitute. If you want an accurate number, measure while erect.