Measuring

How to Measure Penis Size Correctly: BPEL, NBPEL, and Girth

August 4, 2026 · 7 min read

Bone-pressed erect length (BPEL) is the standard: with a full erection, press a rigid ruler into the pubic bone at the base, lay it along the top of the shaft, and read at the tip. That is how measurements are taken in research, which makes it the only number you can honestly compare against published data — the 2015 review by Veale and colleagues in BJU International, which pooled measurements of 15,521 men taken by health professionals, reports an average erect length of 5.17 inches (13.12 cm) and an average erect circumference of 4.59 inches (11.66 cm). Everything below is about how to get that number, and how to get the same number twice.

What you need

A rigid ruler with a flat end — not a folding tape, not a cloth tape. A flexible tape measure for girth. A few minutes of privacy and a room at normal temperature. That is the whole list.

Take the measurement in a standing position unless you have a reason not to, and if you change positions between sessions, note it. Sitting, standing and lying down do not produce identical numbers.

How to measure BPEL, step by step

1. Get a full erection. Not partial. This is the single largest source of error, and it is worth being honest with yourself about where you are on the scale — see the erection hardness scale if you want a reference point.
2. Place the ruler on top of the shaft, flat side against the skin, running along the upper surface from base to tip.
3. Press the end of the ruler straight into the pubic bone at the base, above the shaft. Push until you feel the bone stop the ruler. Firm, steady pressure — not a jab, and not a gentle rest. The point is to travel through the soft tissue in front of the bone and stop at the bone itself, because the bone is the one landmark that does not change.
4. Read at the tip, at the point where the glans ends. Do not include foreskin extending past the tip.
5. Read from directly above. Bring your eyes over the ruler and look straight down at it. Reading at an angle is the classic parallax error and it reliably adds length that is not there.
6. Write the number down immediately, along with the date. Memory rounds up.

Repeat the measurement two more times in the same session and take the middle value. If your three readings drift noticeably apart, something in your technique is inconsistent — usually the pressure at step 3.

NBPEL: the same body, a different starting point

NBPEL — non-bone-pressed erect length — is measured exactly the same way, except the ruler rests on the skin surface at the base instead of being pressed in. Nothing else changes.

The difference between the two numbers is the depth of tissue the ruler travels through: the suprapubic fat pad. How deep that is varies with body composition, and it grows at higher body weight — we know of no published figure for the typical gap, so measure both yourself rather than assuming a conversion factor.

Neither number is dishonest. They measure from different landmarks and answer different questions. But the numbers you encounter online skew toward NBPEL, because it is the larger of the two — and because self-reported figures run higher still. In a 2014 study by Herbenick and colleagues in The Journal of Sexual Medicine, 1,661 men measured themselves at home and reported an average erect length of 5.57 inches (14.15 cm) — noticeably above the 5.17 inches (13.12 cm) found when health professionals did the measuring in the studies Veale pooled. Some of that gap is measurement method. Some of it is the well-documented tendency of self-reported numbers to drift upward.

The practical consequence: if you compare your BPEL against a forum average, you are comparing a bone-pressed number against a mix of non-bone-pressed and self-reported ones, and you will come out looking smaller than the data actually says. Use the percentile calculator, which is built on the Veale figures and expects a bone-pressed number, and read what the average actually is before drawing any conclusion.

BPFSL: bone-pressed flaccid stretched length

BPFSL is measured flaccid: grip just behind the glans, pull straight out with firm but not painful tension, hold it steady, and measure bone-pressed from base to tip as above.

Its usefulness is practical rather than symbolic. It requires no erection, so it is easy to standardize, and for most men it lands close to their BPEL. If you are tracking over months, BPFSL gives you a second data point that is not affected by how good your erection happened to be that morning. If the two numbers ever diverge sharply, that is information worth having — but treat it as a rough indicator, not a precise one. Stretch force is not standardized, and two people pulling with different strength get different numbers.

Stop if it hurts. Pain during stretching is not something to push through; if it persists, see a doctor.

How to measure girth

1. Full erection, same as for length.
2. Wrap a flexible tape measure once around the shaft at mid-shaft — halfway between base and glans.
3. The tape should lie flat against the skin, touching all the way around, without pulling tight. Compressing the tissue narrows the reading. This is the most common girth error and it always makes the number smaller than it should be.
4. Read where the tape meets itself, from directly above.

Girth varies along the shaft in most men — often thicker toward the base. Mid-shaft is the convention because it is the most reproducible spot, and it is what the Veale figure of 4.59 inches (11.66 cm) refers to. If you also want a base measurement, record it separately and labeled; do not average the two.

No tape measure? Wrap a strip of paper or a piece of string around the shaft, mark where it overlaps, and lay it flat against a ruler.

Why your number moves when nothing has changed

This is the part most guides leave out, and it is the reason people conclude they are shrinking. Six variables move independently of anything you do:

Erection quality

The biggest one by far. A partial erection reads shorter than a full one, in length and more noticeably in girth. We have no study that puts a number on that gap — treat any difference between two sessions with different erection quality as not comparable.

Pressure at the bone

Press harder, get a longer BPEL. There is no standardized force, so your own consistency is the only control you have. Aim for “firm until the bone stops it” and apply the same pressure every time.

Parallax

Reading the ruler from an angle instead of from directly above adds a few millimeters, and it adds them inconsistently.

Time of day

Body tissues, hydration and blood flow are not constant across the day. Measure at roughly the same time — morning is easiest to keep consistent.

Temperature

Cold shortens flaccid measurements substantially, and it affects erect readings somewhat. A cold room and a warm room are not the same measuring condition.

The fat pad

The suprapubic fat pad sits between the ruler and the bone. It has no effect on BPEL — that is the entire point of pressing to the bone — but it changes NBPEL directly. If your body weight moves by several pounds over months, your NBPEL moves with it while your BPEL stays put. This is a measurement variable, not a target.

How often to measure

Every four to six weeks. Deliberately not more often.

Weekly measuring does not give you more information; it gives you noise at higher resolution. The day-to-day swing described above is large enough to swamp any real change over a one-week window, and watching that swing is a fast route to discouragement on a low day and false confidence on a good one.

Four measurements taken six weeks apart across half a year tell you something. Twenty-four weekly measurements tell you less, more loudly.

When you do measure, standardize what you can: same time of day, same room, same position, same ruler, three readings, middle value, written down with the date. The absolute number matters less than whether the number was produced the same way last time.

A closing note on honesty: measure before you have any interest in the result. Once you have a target in mind, pressure at the bone tends to increase, erections get graded generously, and the ruler starts being read from slightly the wrong angle. Nobody does this on purpose. It is exactly why a written protocol is worth more than a good memory.

Questions

What does BPEL mean?

BPEL stands for bone-pressed erect length: the ruler is pressed into the pubic bone at the base and read at the tip of the fully erect penis. It is the measurement used in clinical research, which is why it is the only number you can compare with the 5.17 inch (13.12 cm) average reported by Veale and colleagues in BJU International in 2015. Any number taken without bone pressure is not comparable to that figure.

What is the difference between BPEL and NBPEL?

NBPEL (non-bone-pressed erect length) is measured from the skin surface at the base, without pushing the ruler in. BPEL is measured from the pubic bone underneath that tissue. The gap between the two is the depth of the fat pad the ruler travels through. It varies with body composition and is larger at higher body weight; there is no published conversion figure, so the two numbers cannot be converted into each other. Neither is fake; they just start in different places.

How do you measure girth correctly?

Wrap a flexible tape measure once around the shaft at mid-shaft, at full erection, so the tape lies flat and touches the skin without compressing it. Read the number where the tape meets itself. In the 2015 Veale review of 15,521 men, average erect circumference at mid-shaft was 4.59 inches (11.66 cm).

How often should I measure?

Every four to six weeks, under the same conditions each time. Measuring more often mostly captures day-to-day variation — erection quality, temperature, time of day, pressure applied — rather than any real change, and a run of noisy numbers is harder to read than four clean ones spread across six months.

Why is my measurement different every time?

Because at least six things change between sessions: how hard the erection is, how firmly you press the ruler into the bone, the angle you read the ruler from, room temperature, time of day, and body weight. A visible swing between two sessions on the same day is common and does not mean anything changed. We have no study quantifying that swing, which is exactly why single measurements are not worth reading into.

Sources

• Veale et al. 2015, BJU International — nomograms from 15,521 men
• Herbenick et al. 2014, The Journal of Sexual Medicine — self-measured dimensions of 1,661 men

Free tool: see where your measurements sit in the distribution →

Keep reading

• What Is the Average Girth? What the Clinical Data Shows Average erect girth is 4.59 inches (11.66 cm) — from 381 clinically measured men in a 2015 review. What that means, where to measure, and why girth is not diameter.
• What Is the Average Penis Size? What the Measured Data Shows The average erect penis is 5.17 inches (13.12 cm) long and 4.59 inches (11.66 cm) around, based on men measured by clinicians rather than by themselves.
• The Erection Hardness Scale (EHS): How to Rate Your Own Erections The Erection Hardness Score is a validated four-point scale. What each grade means, how to score yourself honestly, and what a series of scores can tell you.