To measure penile size accurately, you need a rigid ruler for length and a flexible tape (or string) for girth, and you should measure while fully erect. The most reliable method, used in clinical settings, involves pressing the ruler against the pubic bone at the base of the penis and measuring to the tip of the glans. This is called the “bone-pressed” technique, and it’s considered the standard because it accounts for differences in body fat and gives a consistent, reproducible number.
How to Measure Length
Use a rigid ruler, not a flexible tape, for length. A flexible tape can follow curves and contours in ways that inflate the number. Place the ruler along the top of the penis (the side facing your abdomen), press the end firmly against the pubic bone, and measure in a straight line to the very tip of the glans. You want a full erection for this measurement, not a partial one.
Pressing against the pubic bone matters because the fat pad above the base of the penis can hide a significant portion of the shaft. In men with higher body weight, this pad of tissue can envelop enough of the shaft to make the externally visible length considerably shorter than the actual structural length. The bone-pressed method bypasses that variable entirely, giving you the true length regardless of body composition. Research confirms that measuring from the pubic bone to the tip of the glans is more accurate and reliable than measuring from the skin surface alone.
If you want to know your “visible” or “non-bone-pressed” length, simply place the ruler on top without pressing into the fat pad. The difference between these two numbers tells you how much length is concealed by soft tissue.
Stretched Flaccid Length as an Alternative
If measuring while erect isn’t practical, you can measure stretched flaccid length instead. Grip the glans gently, stretch the penis outward to its full extent without causing pain, and measure from the pubic bone to the tip using a rigid ruler. Clinical studies use this technique as a proxy for erect length, and it’s the standard measurement for diagnosing conditions like micropenis. In adults, a stretched length below 7.5 cm (about 3 inches) meets the diagnostic threshold for micropenis, which is defined as 2.5 standard deviations below the average.
How to Measure Girth
Girth is the circumference of the shaft. Wrap a flexible measuring tape snugly around the thickest part of the shaft, typically just below the head. Read the number where the tape meets itself. If you don’t have a flexible tape, use a piece of string or a thin strip of paper, mark where it overlaps, then lay it flat against a ruler.
Measure girth while fully erect. Flaccid girth varies too much with temperature and arousal level to be meaningful, and it doesn’t correlate well with erect girth.
Factors That Affect Your Measurement
Several things can cause your numbers to vary from one attempt to the next, so it helps to keep conditions consistent.
- Temperature: Cold environments cause the penis to retract. Clinical researchers have noted that measurements taken in cooler rooms produce shorter results than those taken at comfortable room temperature. If you’re measuring flaccid length for any reason, a warm room gives the most representative number.
- Erection quality: A partial erection will give you a shorter, thinner measurement. Clinical studies require a fully rigid erection for inclusion. If you’re not at full rigidity, the result won’t reflect your actual size.
- Body position: Research studies have used both standing and lying down positions, and there’s no consensus on which is more accurate. Standing is the more practical choice at home. What matters more is that you use the same position each time if you’re comparing measurements over time.
- Body weight: The suprapubic fat pad grows with weight gain and shrinks with weight loss. This doesn’t change your bone-pressed measurement, but it does change how much length is visible and functional. Men who lose significant weight often notice a meaningful increase in visible length without any actual structural change.
Where You Fall on the Average
Large-scale reviews of physician-measured data put the average erect length at roughly 12.9 to 14.2 cm (about 5.1 to 5.6 inches), depending on the study population and whether erections were naturally achieved or pharmacologically induced. The average erect circumference is approximately 12.2 to 12.7 cm (about 4.8 to 5.0 inches). These numbers come from clinical measurements, not self-reported surveys, which tend to skew higher.
Normal variation is wide. A standard deviation of about 2.7 cm for length means that roughly two-thirds of men fall within an inch of the average in either direction. Being above or below the mean by a centimeter or two is completely typical.
Tips for a Consistent Measurement
If you’re measuring to track a change over time, to size a medical device like a condom, or simply out of curiosity, consistency is the goal. Measure at the same time of day, in a warm room, while standing, at full erection, using the bone-pressed technique with a rigid ruler. Take three measurements on different occasions and average them. Single measurements are unreliable because erection quality, arousal level, and even time since last ejaculation can introduce small variations.
For condom sizing, girth is the more important number. A condom that’s too tight can break or feel uncomfortable, while one that’s too loose can slip. Most condom brands list a “nominal width,” which is the flat width of the condom laid on its side. Multiply that number by two to get the approximate circumference it’s designed for, then compare it to your girth measurement.