Several studies have measured penile size in various samples. Some authors have tabulated studies of penile size 6 - 13 . Two studies have produced a nomogram for their samples 9 , 11 . A nomogram is a graphical representation of the numeric relationship between two variables. Such a tool may be a helpful for clinicians to counsel men who desire to know where they lie within a normal distribution or to establish one's change in size percentile following a procedure claiming size augmentation. Building such a nomogram may also be of academic interest, e.g. to investigate the discrepancy between individuals perceived and actual penis size; or to investigate the relationship between condom failure and penile dimensions 14 . However, there have been no formal systematic reviews of penile size measurements and no attempts to combine the existing data into a definitive nomogram for flaccid and erect penile length and circumference (or ‘girth’). Therefore the aim of the present study was to create such nomograms of male penis size measurements across all ages and races, and to conduct a narrative review of the correlations reported. The Preferred Reporting Items for Systematic Reviews and Meta‐Analyses (PRISMA) method of reporting was used 15 .

The measurement of penis size may be important either in the assessment of men complaining of a small penis or for academic interest. Men may present to urologists or sexual medicine clinics with a concern with their penis size, despite their size falling within a normal range. This type of concern is commonly known as ‘small penis anxiety’ 1 or ‘small penis syndrome’ 2 . Some men who are preoccupied and severely distressed with the size of their penis may also be diagnosed with body dysmorphic disorder (BDD), where the preoccupation, excessive self‐consciousness and distress is focussed on their penis size or shape 3 , 4 . The diagnosis of BDD or small penis anxiety excludes 2.28% of the male population who are abnormally small as less than 2 standard deviations (sds ) below the mean 5 .

Where there were more than two studies reporting one of the five types of penis size measurement, the ratio of between study variance to total variance (intraclass correlation, ICC) was calculated as an index of heterogeneity of studies. High ratios of between‐study variance would indicate measures are is less reliable for a particular measurement dimension.

To construct penis size nomograms a weighted mean (by the number of men in each study) and pooled sd were calculated. Using the overall weighted mean and sd, 20 000 observations were simulated from the normal distribution to generate the nomograms. The cumulative normal distribution for each dimension gave population percentiles based on penis length (flaccid, stretched flaccid and erect) and girth (flaccid and erect). All nomograms were generated and edited in the package ggplot2 in R v.30.

Studies followed a penis size measurement procedure described by Wessells et al. 5 . None of the studies had used inter‐rater reliability when taking measurements. Some described training procedures to ensure consistency between different raters 6 . Some described repeated measures used to ensure accuracy 18 . None of the studies describe details on how they recruited their samples, e.g. how many refused to participate, in order to determine whether or not they were representative of the population recruited.

Data extracted from each study included the authors; publication date; population studied; race; the number of participants ( n ); mean and sd of the age and range of participants; the measurement procedure; the mean, sd and range of (i) flaccid length, (ii) stretched flaccid length, (iii) erect length, (iv) flaccid circumference of the shaft, and (v) erect circumference of the shaft at either the base or the mid‐point but not under the glans.

All the correlations between penile dimensions and somatometric parameters were either inconsistent or weak. The most consistent and strongest significant correlation was between flaccid stretched or erect length and height, which was found in four studies and ranged from r = 0.21 to 0.31 and in one study was 0.61.

Seven studies 5 , 7 - 9 , 21 , 22 , 24 found no significant correlation between age and penile size. Two studies 13 , 23 reported that age was weakly positively correlated with flaccid circumference ( r = 0.05 and 0.19, respectively) but not flaccid length. Schneider et al. 25 found a small group of younger men (aged 18–19 years) to be significantly smaller in their flaccid length and erect circumference but not erect length compared with a group of men aged 40–68 years.

A nomogram was constructed for each key variable: flaccid, flaccid stretched and erect length in Figure 2 , and flaccid and erect girth in Figure 3 . The mean and sd for each of the measures are shown at the bottom of Table 1 . The ratios between the mean of each of the domains is found in Table 2 . Of note is that the mean stretched length and erect length were near identical and that mean flaccid length and circumference was near identical.

The ratio of between study variance to total variance (ICC) was relatively low for erect length (0.2), flaccid girth (0.21) and flaccid length (0.26) but was somewhat larger for stretched length (0.58). For the latter, two studies 19 , 20 had a mean stretched flaccid length of >16 cm and two had a mean of <10 cm. This suggests there may be greater unreliability in the measure of flaccid stretched length.

Discussion

In all, 20 studies, with up to 15 521 males, meeting the inclusion and exclusion criteria were found. Five definitive nomograms for the flaccid and erect penis size measurements with a mean and sd were created. Strengths of the present review are that strict inclusion and exclusion criteria were used and there was (modest) homogeneity in the studies. Consistent weak but significant correlations between height and stretched flaccid or erect size were found. However, correlations with other somatometric parameters were either inconsistent or weak.

Wessels 5 suggested that beyond 2 sds below the mean should define a candidate for penile augmentation (2.28% of the male population), which we found was <6 cm in the flaccid length and <9.5 cm in the stretched length. A micropenis, however, is defined as <2.5 sds below the mean (0.14% of the male population), which was <5.2 cm in flaccid and <8.5 cm in the stretched length.

Stretched flaccid length appears to be an excellent estimate of erect penile length, which for some individuals presenting to clinical settings, may indicate that it may not be necessary to measure erect length as well as flaccid size. However, there was greater variability in the measures, which suggests less reliability. This was found by Chen et al. 30 who reported that a minimal tension force of ≈450 g during stretching of the penis was required to reach a full potential erection length and that the stretching forces exerted by a urologist in their clinical setting were experimentally shown to be significantly less than the pressure required. This may account for a discrepancy observed in three out four of our present studies in Table 1, which measured stretched and erect length simultaneously and found that the erect length was longer than the stretched flaccid length. There is therefore a greater risk of bias in measuring the stretched length if insufficient pressure is applied and the greatest need for training and measuring inter‐rater reliability.

It is not possible from the present meta‐analysis to draw any conclusions about any differences in penile size across different races. Lynn 31 suggest that penis length and girth are greatest in Negroids (sub‐Saharan Africans), intermediate in Caucasoids (Europeans, South Asians and North African), and smallest in Mongoloids (East Asians), but this is based upon studies that did not meet our present inclusion and exclusion criteria. The greatest proportion of the participants in the present meta‐analysis were Caucasoids. There was only one study of 320 men in Negroids and two studies of 445 men in Mongoloids. There are no indications of differences in racial variability in our present study, e.g. the study from Nigeria was not a positive outlier. The question of racial variability can only be resolved by the measurements with large enough population being made by practitioners following the same method with other variables that may influence penis size (such as height) being kept constant. Future studies should also ensure they accurately report the race of their participants and conduct inter‐rater reliability.

Herbenick et al. 32 found from their self‐report data of 1661 men, a mean erect penile length of 14.15 cm and a mean erect penile circumference of 12.23 cm. This is about 1 cm larger than the mean erect length and 0.6 cm larger than that the mean circumference from our nomograms. This might be dismissed as the unreliability or bias of self‐report but they argue that their sample was more accurate, as the data were reported anonymously over the internet and were motivated to obtain a condom that fitted their erect penis. Their data also suggest that the mode of getting an erection may influence erect penile dimensions (e.g. being with a sexual partner at the time of the measurement) and that this may be more accurate than self‐stimulation especially in a clinical setting.