This study aimed to establish a reference range of penile length and circumference of adult males in China, and to compare the penile dimensions of different ethnical backgrounds. To do this, penile length and circumference measurements were obtained from 5196 healthy males attending the Urology Counseling Clinic. The mean value of penile dimensions was a flaccid length of 6.5±0.7 cm, a stretched length of 12.9±1.2 cm and a flaccid circumference of 8.0 ±0.8 cm. In the subgroup of 311 males, the mean erectile length was 12.9±1.3 cm and the mean erectile circumference was 10.5±0.9 cm, the mean flaccid and erectile glans lengths were 2.7±0.3 and 3.4±0.4 cm, respectively, and the mean flaccid and erectile glans diameters were 2.6±0.2 and 3.4±0.4 cm, respectively. We found that flaccid penile length and circumference varied among different ethnicities. This study established a reference range for penile dimensions, which will help when counseling patients worried about their penile size or seeking penis enlargement surgery. We also found that penile dimensions are different in different ethnicities, but further investigations are needed to validate this.
The definitions of penile length have become of increasing interest in different countries and cultures. Various studies have reported penile dimensions in different countries (Table 1), but due to variations in patient selection and the methodology used to generate the measurements, the results vary significantly. Therefore, it largely remains unknown what the normal variations of penile dimensions are, or what differences exist in penile dimensions in different countries and ethnic backgrounds. Moreover, to date, there is no convincing report on this topic from China.
China contains 56 nationalities, each with its own geography, language, physical characteristics and ancestry. Ethnic Han accounts for about 90% of the overall population and as such, other ethnic groups in China are regarded as minorities. Yunnan Province is an ethnically plural region, which contains 52 of these ethnicities; therefore, we chose Yunnan Province to conduct a large, single-center survey to evaluate normal variations of penile dimensions among different ethnic groups.
From January 2011 to January 2013, we prospectively measured the penile length and circumference of men attending a Urology Counseling Clinic (excluding those who refused to participate or did not meet inclusion criteria). A total of 5196 males, aged 18- to 60-years-old were recruited. All measurements were taken by one urologist to minimize interobserver error. All penile dimensions were measured twice and their means were recorded. Genital abnormalities were detected by history and physical examination; men with penile abnormalities such as Peyronie disease, penile curvature, cryptorchidism or hypospadias were excluded from the study. Verbal consent was obtained from all participants before measurements were taken.
A subgroup of 311 participants provided erect penile length and circumference. Penile length and diameter, and glans length and diameter were measured by the urologist at the flaccid and erectile state after a period of privacy and self-stimulation with video.
The participants were kept in the supine position. Penile length was measured by a straight edge ruler, and penile circumference and glans dimensions were measured using a vernier calipers. The flaccid penile length was measured as the linear distance along the dorsal side of the pubo-penile skin junction to the tip of the glans (Figure 1a). The stretched flaccid length was measured as the distance from the pubic bone to the tip of the glans, under gentle painless extension of the penis (Figure 1b). The erect length was measured as the distance from the pubic bone to the tip of the glans (Figure 1c). The penile circumference was measured at the middle of the shaft (Figure 1d). The glans length was measured as the distance from the corona to the tip of the glans (Figure 1e), whereas glans diameter was measured as the linear distance between two points on the circumference of the glans that passes through its center (Figure 1f).
The age, height, weight and ethnic backgrounds of all participants were recorded. Body mass indices (BMI) were then calculated. Penile extensibility, which is the difference between the length of the flaccid penis and the penis submitted to a maximal constant traction, was also calculated.
The examination room was kept quiet, comforting and private. The temperature was set to 24 °C, to alleviate any anxiety and to permit relaxation of the external genitalia.
Data analysis was performed using the Statistical Package for Social Sciences, (version 17.0; Chicago, IL, USA). Statistical tests were applied using two-tails, at a 5% level of significance. Descriptive statistics as mean, s.d. were recorded. Correlations of different factors were performed using Pearson’s analysis, and the means of different ethnicities were compared using one-way analysis of variance and Dunnett method. The Kruskal–Wallis test was performed to detect variance non-homogeneity.
The mean penile dimensions of all participants measured were: a flaccid length of 6.5 cm, a stretched length of 12.9 cm and a flaccid circumference at the penile mid-shaft of 8.0 cm (Table 1). These parameters were rounded to the nearest 0.5 cm. Age, weight, height and penile measurements in the sample of 5196 adult males are reported in Table 2. The penile dimensions of different ethnicities are shown in Table 3.
The stretched length and flaccid circumference of the penis’ in the subgroups of 311 males and 4885 males are not significantly different. Penile and glans dimensions of the men participating in erectile penile measurements are shown in Table 4.
Analysis correlations of penile dimensions, age and somatometric parameters (Table 5) revealed that: (a) age was negatively correlated with flaccid (r=−0.119, P=0.037), stretched (r=−0.136, P=0.016) and erectile lengths (r=−0.144, P=0.011).: (b) Body mass index was negative correlated with flaccid (r=−0.135, P=0.017), stretched (r=−0.128, P=0.025) and erectile lengths (r=−0.142, P=0.012).: (c) penile dimensions were not correlated with height or weight.
One-way analysis of variance showed that flaccid circumference (P=0.009) was different in different ethnicities. Ethnic BuYi and Zhuang exhibited larger values, whereas ethnic NaXi and AChang exhibited lower values, for flaccid circumference compared with other ethnic groups. The Kruskal–Wallis test indicated that flaccid penile length (P=0.04) was also different in different ethnicities, with ethnic Man, BuYi and Dai showing the highest values and ethnic Shui, the lowest value. In addition, penile extensibility was correlated with flaccid length (r=0.501, P=0.001) and stretched length (r=0.880, P=0.001), but was not correlated with age (r=0.005, P=0.699).
Regression modeling for EL (erected length) was performed using stretched length values. The adjusted R-square of the model is 0.956 (R2=0.956) and was found to be significant (P<0.01) as determined by analysis of variance. A linear regression model for the EL was formed, EL=(0.936+0.761 × (SL)).
China is an ethnically plural country, and different ethnicities have their own societal and physical characteristics. Thus, it is interesting to investigate whether penile dimensions are different among different ethnicities. In the present study, we have described the normal variations of penile length and circumference in the Yunnan province of China. These data will prove useful to clinicians, who counsel patients worried about penile size. To our knowledge, this survey is the largest of its type ever conducted, with the highest diversity in ethnic groups. Moreover, the study was conducted in a single center, where the effects of selective participation and varying penile measurement methodology could be avoided.
In the present study, we found that differences exist in flaccid penile length (P=0.04) and circumference (P=0.009) between 22 ethnicities. However, no differences exist in stretched length. Due to large P-value (P=0.04) in flaccid penile length, and taking the small sample size of minority ethnicities into consideration, further investigation should be performed to validate these results. Previous studies have focused on penile dimensions in different populations, yet none describe the relationships between penile dimensions and ethnicity or race. Thus, our results may prove very helpful to urology clinicians and counselors offering therapy to individuals worried about penile length. Notwithstanding our data, a worldwide study is needed to determine if racial differences can mediate penile dimensions.
It should be noted that flaccid penile length was lower in China, than in other countries (Table 1), whereas the stretched length was similar. Our results of erectile penile length were also similar to that reported in other countries.1, 2, 3 These differences may suggest race variations or methodologies; however, there is no internationally recognized standard penile measurement technique available, and we hope that the detailed description (Figure 1) of our measurement technique enables other investigators to achieve similar measurements.
In previous studies, normal penile length borderline values were defined as below the mean −2.5 s.d.1, 4 Micropenis is defined as flaccid length lower than 4.0 cm and stretched length lower than 7.5 cm.1 As such, less than 5% of Chinese adult males would be diagnosed as having true micropenis; however, although the incidence of micropenis was low, the actual number of affected patients may be very high, as China has the largest population in the world. Shamloul5 performed a study on 92 men complaining of a short penis. Interestingly, he reported that due to misleading sexual conception, his patients often had a feeling of having a short penis, when in fact their penile length was normal.5 Therefore, it is important to inform the general population of the correct information regarding penile dimensions, especially considering today’s internet era. In this respect, our study could be used to counsel adult men and help relieve unnecessary concerns of penile inadequacy.
Some studies6, 7, 8 report correlations of penile dimensions and somatometric parameters. Ponchietti et al.6 showed that penile length was negatively correlated with body mass indices, which was confirmed in our study. However, their studies also indicated a positive correlation between penile length and height, and a negative correlation between penile length and weight, which were not found in our study. Nevertheless, Mehraban et al.7 showed that penile length has a positive correlation with weight. In addition, some reports9 reveal that penile length was negatively correlated with age, which is validated in our study; however, another showed7 that penile length has a positive correlation with age. In the present study, we observed that penile length was negatively correlated with body mass indices and age (the r-value varies from −0.119 to −0.144), and no correlations were found between penile dimension, and weight and height. As such, correlations of penile dimensions and somatometric parameters are still ambiguous, and we cannot exclude the effects of variability among different study samples, age groups or ethnic backgrounds.
In our study, penile extensibility is positively correlated with penile length, especially stretched length. This is in contrast with a previous study, which showed no correlation between penile extensibility and flaccid length.6 In addition, it has been reported that that penile extensibility decreases with age;10 however, our results suggest that penile extensibility does not generally decrease with age. This may due to the health of the males we recruited and their sub-60-years age profile.
Traditionally, intracavernous injection with prostaglandin E1 is an effective method to obtain full penile erection. However, in our study, all 311 participants were healthy males without erectile dysfunction, and all could achieve full erection with self-stimulation. We observed that flaccid and stretched penile lengths were strongly correlated with erectile penile length. Moreover, compared with other studies, our measurements of erectile penile length (12.9 cm) were similar to that in the United States of America (12.49 cm),1 India (13.01 cm)3 and Israel (13.6 cm).2 Thus, we may consider stretched penile length as a good predictor to determine erectile penile length, while may be especially useful when unable to measure erectile penile size.
There is a lack of information regarding glans dimensions. Our results reveal that glans length and diameter are highly correlated with circumference, whereas no correlations were found with penile length or somatometric parameters. Our mean measurement of flaccid glans length (2.7 cm) is similar to those made in Iran (3.04 cm);7 however, it was lower than those made in Greece (4.4 cm).9 This is the most comprehensive report describing glans dimensions, and may prove useful for clinicians especially when performing penile augmentations, or counseling patients concerning about their penile dimensions.
This study was conducted in a single center where participants were not drawn directly from the general population. Thus, the risk of investigator bias in sample selection cannot be excluded. Moreover, although our sample size is the largest ever reported for this type of study, the sample size of some ethnic groups in our survey is small, and this may affect our results when comparing differences in the penile dimensions of different ethnicities.
In conclusion, our study is the first to establish a comprehensive reference range for penile dimensions in Chinese men. We found that penile dimensions differ across ethnicities. Our study may be helpful in counseling patients who are worried about their penile size or seeking penis enlargement surgery.
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We would like to thank Mrs Yan Zhang, associate professor, Shanghai Institute of Planned Parenthood Research, Shanghai, China, for her valuable review of the statistics of this article before submission.
The authors declare no conflict of interest.
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Chen, X., Li, R., Yang, H. et al. A comprehensive, prospective study of penile dimensions in Chinese men of multiple ethnicities. Int J Impot Res 26, 172–176 (2014). https://doi.org/10.1038/ijir.2014.9
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