Healthcare professionals may be asked by men nervous about their penis size whether they are normal.

However, we are not able to offer much in terms of reassurance because there is very little information about the normal distribution of penis length based on objective measurements on a large enough number of men to make it representative. 

This systematic review set out to answer just that. In addition, it aimed to produce a nomogram which shows the normal distribution of penis measurements.

The eligibility criteria for included studies were: objective measurements of penis size made by a healthcare professional; sample size ≥ 50 patients; age ≥ 17; mean and standard deviation (SD) provided; flaccid or erect measurement measured from root of penis (with pubic fat pushed to bone) to tip of glans (meatus) on dorsal surface; flaccid stretched length was measured as above while maximally extending the penis; flaccid or erect circumference (or girth) measured at base or mid-shaft of penis; published in the English language.

Studies that used measurements from cadavers, patients with congenital or acquired abnormalities (e.g. Peyronie’s disease, phimosis), erectile dysfunction and those seeking augmentation as well as self-reported measurements were not included.

The authors agreed on a search strategy to look for primary studies using databases such as Ovid Medline, Embase and PsychINFO. The titles and abstracts were screened by one author and full text by two. A total of 20 studies were included with dimensions measured in 15,521 men.

A weighted mean and pooled SD were calculated in order to create penis size and girth nomograms for erect, stretched and flaccid states, see table 1.

A summary was also given for correlations between penile dimensions and other measurements such as height and BMI as these were reported by some studies.

There were weak correlations between other somatometric parameters and penile dimensions; the only consistent correlation was between flaccid stretched or erect length and height.

There are clinical implications from this study. First, the findings can help to define which men may be suitable candidates for penile augmentation; this is usually defined as those below 2 SD below the mean which is < 6 cm in the flaccid state and < 9.5 cm in the stretched length from this study.

In addition, a ‘micropenis’ is defined as below 2.5 SD below the mean, which is < 5.2 cm in the flaccid state and < 8.5 cm in stretched length.

Another practical implication is that the stretched flaccid penile length appears to be closely correlated with erect penile length. Hence, men presenting to clinical settings can have their penis measured in the flaccid state.

Dr Richard Ma