To measure your penis with a ruler, place the flat edge against the top of the shaft where it meets your body, press gently until the ruler touches the pubic bone, and read the measurement at the tip. This “bone-pressed” method is the standard used in medical studies and gives the most consistent, accurate result. Below is a step-by-step breakdown covering both length and girth, plus how your numbers compare to published averages.
What You Need
A rigid ruler works well for length. A flat, straight ruler is actually what most clinical researchers use because it’s easy to hold steady along the top of the shaft. For girth, you’ll need a flexible measuring tape (the kind used for sewing) or a piece of string you can later hold against the ruler.
How to Measure Length
Measure when fully erect. Stand upright or stand against a wall so your body is straight. Place the ruler along the top of the penis (the side facing the ceiling when you look down). Push the end of the ruler back through any soft tissue at the base until it rests firmly against the pubic bone. Read the measurement at the very tip of the head.
This is called the bone-pressed method. It bypasses the fat pad that sits over the pubic bone, which can vary in thickness from person to person and change with weight fluctuations. Pressing to the bone captures the true anatomical length of the internal structures and is the technique used in virtually every published study on penis size. If you want to compare your number to any average or size chart, this is the measurement to use.
You can also take a non-bone-pressed reading by simply resting the ruler on the surface skin without pushing in. This reflects more of what a partner sees, but it will read shorter, especially if you carry extra weight around the midsection. Researchers note that discrepancies between the two methods are largest in overweight individuals.
Measuring When Erect Isn’t Possible
If you need a rough estimate without a full erection, measure the stretched flaccid length using the same bone-pressed technique: hold the head gently and stretch the penis outward to its full comfortable extent, then measure from the pubic bone to the tip. Research published in The Journal of Urology found that stretched flaccid length predicts erect length with about 79% accuracy, making it a reliable stand-in used in clinical settings.
How to Measure Girth
Girth is the circumference, or the distance around the shaft. Wrap a flexible measuring tape snugly around the thickest part of the shaft, which for most people is just below the head. Read where the tape overlaps. Don’t pull the tape tight enough to compress the skin; you want a snug but comfortable wrap.
If you only have a ruler, use a piece of string or a thin strip of paper instead. Wrap it around the thickest point, pinch or mark where it meets, then lay it flat against the ruler to get the number. This gives you the same result as a flexible tape.
How Your Numbers Compare
A large meta-analysis reviewed by King’s College London pooled data from over 15,500 men measured by health professionals. The averages:
- Erect length: 5.16 inches (13.12 cm)
- Erect girth: 4.59 inches (11.66 cm)
- Flaccid length: 3.61 inches (9.16 cm)
- Flaccid girth: 3.66 inches (9.31 cm)
These numbers come from measurements taken by clinicians, not self-reported data, so they’re considered more reliable than survey-based figures. Most men fall within about an inch above or below these averages.
Using Your Measurements for Condom Sizing
Girth matters more than length for condom fit. A condom that’s too tight can break or feel uncomfortable, while one that’s too loose can slip off. Standard condoms from major brands are designed for a girth of roughly 4 to 5 inches and a length of 5 to 7 inches. If your girth falls below or above that range, look for snug-fit or large-fit options respectively. Most condom brands list the nominal width (the flat width of the condom before it’s unrolled) on the packaging, which you can match to your circumference for a better fit.
Tips for a Consistent Reading
Measure at the same time of day and under similar conditions if you want to track or compare over time. Erection quality fluctuates with arousal level, temperature, stress, and time of day, so a single measurement is a snapshot. Taking two or three readings on different days and averaging them gives you a more reliable number.
Always measure along the top (dorsal) surface. Measuring along the underside adds length because of the way the shaft curves and where the scrotum attaches. If your penis has a noticeable curve, hold the ruler along the top and measure in a straight line from the pubic bone to the tip. The straight-line distance is what’s used in research and for practical sizing purposes. For a pronounced curve (more than about 30 degrees), a flexible tape laid along the outer curve will give a longer reading that reflects the actual surface your partner experiences, but this isn’t directly comparable to published averages.