This study aimed to determine the penile size and its correlation with somatometric parameters in physically normal Iranian adult men. To do this, a random sample of 1500 normal men aged between 20 and 40 years underwent tape measurements of penile dimensions in the stretched state under the same condition. The mean total penile length was 11.58±1.45 cm, the mean glanular length was 3.04±0.33 cm and the mean girth was 8.66±1.01 cm. Multivariate regression analysis showed that penile dimensions are significantly correlated with age (P=0.018), height (P<0.001) and index finger length (P<0.001). This analysis provided no evidence for significant effect of waist/hip ratio and weight on penile dimensions. As the penile augmentation is still in its experimental stage and its indications have not yet been clearly established, providing standardized data on penile dimensions seems to be necessary to make convenient decisions in the counseling and/or treatment of people with short penis concerns.
Measurement of penile length is necessary in many situations. Some of these include diagnosis of micropenis (including pituitary and hypothalamic hormone deficiencies), anatomic malformations of the genitalia, defining the situations requiring penile-lengthening procedures, evaluating the results of medical or surgical intervention of the penis, and experimental studies.1
In the everyday clinical practice, urologists quite often have to deal with young patients who present with complaints of inadequate size of their external genitalia.2 Concerns over penile size and a desire for a longer penis are common in the male population and the number of male patients seeking andrological consultation for the problem of ‘short penis’ is increasing.3 Most commonly these patients are otherwise physically normal males, who seek validation of their sexual function and fertility potential, true confirmation of genital organ normality and adequacy. Furthermore, the definition of normal penile size is currently of considerable importance in the diagnosis and treatment of sexual dysfunction and in the light of the claims of penile augmentation in the lay press.4, 5
A review of previously published urologic surveys in different populations reveals an absence of universally acceptable parameters and standardized criteria on the proper size of the external genital organs. This poses major difficulty in the counseling and/or treatment of young adult men with worries of sexual inadequacy.2
In our country, Iran, standardized and proper criteria on the size of external genitalia is not available; thus, we decided to conduct this study to determine the penile length profile of the physically normal adult Iranian males aged between 20 and 40 years. In the present study, we also aimed to evaluate the dependence between penile dimensions and some somatometric/anthropometric parameters in this population. The obtained results would aim to provide a framework for urologists in the counseling and/or treatment of adult men with the described concerns.
Sampling technique and study sample
In this survey, 1500 Iranian healthy men aged between 20 and 40 years old were randomly recruited. The random selection was performed using a table of random numbers. According to some reports, over 10 millions people live in Tehran and suburbs now. This population is composed of different ethnicities of Iran distributed in its 22 municipality districts. Thus, a large sample of 1500 adult men in this city may be considered as a representive and reasonable sample for the same population in Iran.
Certain clinics in 22 districts of Tehran were approached and set as the examination venue for interested healthy volunteers of 20–40 years of age if they met the inclusion/exclusion criteria. To select the study sample, a multistage sampling technique was used. In the first stage, one clinic was randomly selected in each municipality district of Tehran using a simple random sampling method. In the second stage, in each selected clinic at least 25 healthy men were recruited. To choose the study sample in each clinic, we chose at least 25 random numbers between 1 and 100 (proportional to sample size in each clinic) and then according to the selected numbers the study samples were selected among the consecutive referrals to each clinics. The study objectives were exactly explained to each selected man and then he was recruited if he signed the study consent. As only few numbers of these persons (less than 10 men) did not accept to participate in our survey, the selected adult men may be considered as a good random sample for the healthy adult men population.
At the time of measurement, all the selected subjects appeared physically normal, with normal sexual function (erection and ejaculation), with no history of infertility, cryptorchidism, hypospadias or any surgery other than circumcision, or any inflammatory/malignant condition of the penis or the testicles.
Training and reliability analysis
In each clinic, only a trained caregiver measured the penile size. The principal investigator invited the caregivers and held training sessions for them by examining volunteers in front of them and then observing them to do the measurement themselves. For reliability assurance, the measurements by the caregivers were rechecked by the investigators in some volunteers before the conduction of the study.
To assess the interexaminer reliability, five caregivers were randomly selected and the penile sizes of 10 volunteers were measured by them. Then, a random effect model was used to assure the interexaminer reliability according to the method presented by Fleiss.6 The estimated reliability coefficient was R=0.953, which indicated a high interexaminer reliability among these caregivers. In addition, we used the method discussed by Fleiss6 to evaluate the intraclass reliability. To do this, a caregiver was randomly chosen and the penile sizes of five volunteers were measured by four times by him. The obtained intraclass correlation coefficient was R=0.991, which indicated a high intraexaminer reliability in this study.
During the study, the study clinics were visited on a regular basis and quality of examination was checked again by the investigators. This was believed to be crucial for the concordance of the measurements.
Tape measurement of penis, glans and penile circumference was made in centimeters with one decimal point. To measure the total penile length, we placed the butt of a rigid tape measure tool on the pubic skin over the dorsum of the fully starched penis held by the other hand and stretched once. The distance between the pubic skin and the external urethral meatus was recorded. The glans length was measured from the corona to the external urethral meatus level. The penile circumference or girth was measured at the midshaft. The height and weight were measured as routine.
The waist circumference was measured at the umbilical level and the hips circumference was measured at the level of the anterior–superior iliac spines. The length of the extended index finger was measured from the metacarpophalangeal joint to the tip of the distal phalanx, excluding the nail tip.
The examination room had to be quiet, comforting, and with the temperature between 20 and 25°C to alleviate any anxiety and to permit relaxation of the external genitalia.
The data analysis was performed using the Statistical Analysis System, version 9.1 (SAS 9.1). Descriptive statistics, Pearson's correlation coefficient, univariate and multivariate regression models were utilized for data analysis. In the multivariate modeling process, the generalized estimating equations (GEE) methodology was used to account for the correlation between the response data.
As stated earlier, a random sample of 1500 Iranian physically normal adult males were assessed in this study. Table 1 shows the characteristics of the study sample. In addition, Table 2 shows the descriptive statistics for the penile dimensions among this sample.
Using the Pearson's coefficient of correlation, we found a significant and positive relationship between these penile measurements. The correlation between total penile length with glanular length and girth were 0.472 (P<0.001) and 0.183 (P<0.001), respectively. In addition, glanular length and girth were statistically correlated with a Pearson's correlation coefficient of 0.315 (P<0.001).
We also determined the correlation between these penile measurements and the described somatometric parameters. Table 3 shows these findings.
According to the results of Table 3, age was significantly and positively correlated with girth (r=0.197, P<0.001), but there was no significant correlation between age and total penile length (r=−0.006, P=0.808). In addition, we found no significant relation between age and glanular length (r=0.033, P=0.204). Moreover, weight, height and index finger length showed statistically positive and rather strong correlation with all penile dimensions (all the P-values were below 0.001). There was also an inversely significant association between waist/hip (W/H) ratio and glanular length (r=−0.197, P<0.001), but we found no evidence for the relationship between W/H ratio and total penile length (r=−0.046, P=0.074) as well as W/H ratio and granular length (r=0.018, P=0.479).
We also assessed the association between the explanatory variables (age, weight, height, W/H ratio and index finger) and the penile dimensions using univariate and multivariate regression models. Table 4 shows the obtained results.
The univariate regression analysis showed that index finger length is an independent and direct predictive variable for total penile length (P<0.001), glanular length (P<0.001) and girth (P<0.001). According to these results, the subject's height was another independent and positive predictive variable for total penile length (P<0.001), glanular length (P<0.001) and girth (P=0.023). This analysis revealed that age has a positive association with girth (P<0.001). Additionally, the subject's weight showed a significant and indirect relation with total penile length (P=0.047). Finally, the significant estimates for W/H ratio provide a strong evidence for the inverse effect of this predictive variable on girth (P=0.003).
In Table 4, we also considered a multivariate regression model for assessing the relationship between penile dimensions (simultaneously) and somatometric parameters. According to the reported results, penile dimensions (total penile length, glanular length and girth) were positively associated with predictive variables age (P=0.018), height (P<0.001) and index finger length (P<0.001). This multivariate analysis provided no evidence for the relationship between penile dimensions and explanatory variables W/H ratio (P=0.370) and weight (P=0.771).
Finally, total penile length was considered to construct a nomogram using 2.5th, 50th and 97.5th percentiles (Figure 1). In different ages, values below the 2.5th percentile and more than 97.5th percentile may be considered as abnormal penile length.
In recent years, the definition of normal penile size has become of increasing interest in performing correct diagnostic assessments and therapeutic choices in patients with concerns regarding penile dimensions.2 A man's self-esteem can be affected by his genitalia profile, mainly penile size, in as much as his self worth may be judged by the ‘adequacy’ of his sexual organs. If a man perceives his penis as inadequate, whether real or imagined, negative feelings invade his interaction with his sexual partner and even his professional associates.7
Recently, the request for penile augmentation is growing in different countries. However, it is claimed that penile augmentation is still in its experimental stage and its indications have not yet been clearly established and many complications have been reported.8 Thus, providing standardized data on penile dimensions seems to be necessary to make convenient decisions in the counseling and/or treatment of people with short penis concerns. Figure 1 provides these guidelines in Iranian 20–40 years old males. In another study, it has been suggested that only men with a stretched or erect length of less than 7.5 cm should be considered candidates for penile lengthening.4 Here, it should be noted that although all the efforts were directed towards including all eligible healthy young adult men, however, some men with self-conceived small genitalia size may have shunned entering the study and this might have affected the results. In addition, there are apparent ethnicity variations among different ethnics such as Fars, Kurd, Azeri and so on in our country, but we found no documented survey about these variations in the related scientific websites. However, we are going to conduct a similar study in different Iranian ethnic groups in the future.
In the present study, we only measured the penile dimensions in the flaccid stretched state. Owing to ethical concerns and religious beliefs in our country, we did not measure penile dimensions in erect state. However, previous studies showed that stretched penile length measurement offers a good alternative to erect and flaccid penile length measurements.1, 4, 9, 10 For instance, regression equations in the study of Sengezer et al.1 showed that penile stretched length is a good predictor for penile flaccid and erect lengths (R2=65.5 and 65.3%, respectively). In addition, the study of Wessells et al.4 resulted in R2=0.793 for the predictability of penile erect length by stretched length.
We have compiled the results of different surveys from different ethnicities published so far in Table 5. As might be seen, because of differences in measurement technique, age and the health status of the study samples, one could not relate the apparent difference in the measurements to the ethnicity factor only. However, our results are close to the Greek and US studies.2, 4 In addition, comparing the results of the present study with other Asian surveys shows that penile size in the flaccid stretched state in Iranian adult men (11.58 cm) is between recorded sizes for the Jordanian20 (13.50) and Korean8 (9.6 cm) normal adult men.
In the previous decades, numerous urologic studies have focused on penile measurements in different populations, but few studies are available about the relationship between penile measurements and different explanatory variables such as somatometric parameters. As penile length and circumference correlate with anthropometric parameters such as weight, height, W/H ratio and index finger length, we considered these parameters as bodily measures, that display a wide extent of normal variability along the general population. A study on 52 Greek males aged 19–38 years revealed that the glanular and total penile lengths are insignificantly inversely correlated to age, weight, BMI and W/H ratio and positively to height and correlated positively (statistically significant) with index finger length.2 In addition, a study on 3300 young Italian males aged 17–19 years showed that penile measurements (length and circumference at the midshaft) are correlated to height, weight and BMI.18 In another interesting survey, the relationship between shoe size and penile length was studied by Shah and Christopher.21 They concluded that the supposed association of penile length and shoe size has no scientific basis. In our study, univariate regression analysis showed significant and positive relationship between total penile length and subject's height and index finger length and negative relationship between total penile length and weight. We did not attempt to include the pubic fat pad in our measurements. This may explain why there is a negative effect of weight on total penile length. It is well known that weight gain increases the amount of the supra-pubic fat pad, which can cause a relative decrease in penile length. In our study, another univariate regression analysis revealed statistically significant and positive association between glanular length and subject's height and index finger length. Moreover, similar analysis showed that age, height and index finger length had significant and direct effect on girth. Finally, W/H ratio was the only significant and inverse effective factor on girth.
We could not find a similar study with the multivariate analysis of penile measurements and anthropometric parameters in the published articles. In this study, the multivariate regression analysis revealed a direct effect of age, height and index finger length on penile dimensions.
Regarding the results of both univariate and multivariate regression analyses, it can be concluded that index finger length is the best predictive variable among the described parameters. Other studies suggested that finger length may correlate with function or disorders of the male reproductive system.22, 23 This is based on the HOXA and HOXD genes' common embryological control of finger development and differentiation of the genital bud.24 Although the measurements of finger lengths do not have the power to predict the testicular function of adult men, its correlation to penile dimensions have been reported.2
Data from 1500 young adult male provide a range that could be used as a standard by andrologists and other medical practitioners pending a larger nation-wide study. The results demonstrate that like other studies, penile and glanular lengths and girth are somatometric characteristics and as such are related to other anthropometric measures.
We express our special thanks to the volunteers for their patience and the research deputy of Tehran University of Medical Sciences for the financial supports.