Shahid A.A. Khan, Western General Hospital – Urology, Crewe Road, Edinburgh EH4 2XU, UK. e-mail: email@example.com
Study Type – Diagnostic (validating cohort)
Level of Evidence 2a
What’s known on the subject? and What does the study add?
Reference ranges for normal penile length have been reported from several different countries and anthropometric differences have been noted between different nationalities and ethnic backgrounds.
This study describes one of the largest cohorts of men undergoing penile size measurements in Europe and the largest UK study. The range of measurements collected in this study will be of use to clinicians treating men with concerns over penile length, as well as helping to diagnose patients with true micropenis.
• To establish a reference range for adult male genital size in the UK using penile length measurements.
• To compare the reference ranges for normal penile length reported from several different countries and the anthropometric differences noted between different nationalities and ethnic backgrounds.
METHODS AND MATERIALS
• Over 20 months, genital measurements were taken from all men undergoing routine examination in clinics (n= 499) and in operating theatres during examination under anaesthetic (n= 110).
• Using a rigid metric ruler three penile measurements were taken: flaccid pendulous penile length, flaccid penopubic penile length (to the pubic arch) and stretched flaccid penopubic length. In addition, testicular size was measured using an orchidometer.
• The patient’s age and the reason for referral were recorded.
• Statistical analysis was carried out using Pearson correlation analysis.
• Measurements from 610 patients aged 16–90 years were available for analysis.
• The mean penile lengths were: pendulous length 8.7 cm (sd 1.6 cm), penopubic length 10.2 cm (sd 1.4 cm) and stretched length 14.3 cm (sd 1.7 cm). The mean testicular volume was 19.8 mL (sd 5.4 mL) for both left and right testicles.
• Men with penile disease (including phimosis and Peyronie’s disease) had slightly reduced penile length (pendulous −3.3 mm, P= 0.014; penopubic −2.3 mm, P= 0.029; stretched −5.1 mm, P < 0.001) compared with other referral groups (erectile dysfunction, testicular disease, prostate and bladder disease).
• There was no significant correlation between penile length and age or testicular size
• These data establish a reference range for adult male genital size in the UK, which should be helpful for urologists when counselling patients.
A man’s self-esteem can be greatly affected by the perception of his own penile size. Concerns over penile size may not only relate to the erect length, but also to the flaccid penis . It has been suggested that most patients concerned with an inadequate penile size are physically normal , but seek reassurance and validation of their sexual and fertility potential. However, some men will present with a true micropenis and others with psychological disease related to penile size (penile dysmorphophobia).
Several studies have previously been conducted to assess normal penile size [2–16] (Table 1) and suggest variations between genital size in different populations related to ethnicity. We could only find one study with data for men in the UK, which was small (n= 104) and only examined stretched flaccid penile length . The aim of our study was to establish a reference range on genital size for British men. As phallic growth depends on hormonal function we included testicular size measurements to determine if testis size correlated with penile length.
Table 1. Comparative worldwide data on penile length from the literature (excluding self-reported measurements)
Between 1 January 2007 and 14 August 2008, we prospectively measured penile lengths of all men attending the general urology and andrology subspecialist clinics of one consultant (n= 499) in two hospitals, who required routine examination. Additional patient measurements were taken in the operating theatre as part of the examination under anaesthesia of patients who had not previously been seen in these clinics (n= 110). Three penile measurements were predominantly taken by two investigators (RD, 569; BS, 33; others, 6), using a rigid centimetre ruler and the same measurement technique.
The three measurements recorded were:
1The flaccid ‘pendulous’ length, in which the flaccid penile length was measured from the tip of the glans penis to the base of the pendulous penis.
2The ‘pubic arch penile length’, measuring from the tip of the glans penis to the lower edge of the pubic bone above the suspensory ligament insertion.
3The ‘stretched flaccid length’, which is determined as the distance from the pubic bone to the tip of the glans penis under gentle painless extension of the penis.
Penile length measurements were taken at normal room temperature with the patient supine and the legs adducted and before surgery in anaesthetized patients. Only Caucasian, British men were included in the study.
Additionally, testicular size was measured using an orchidometer. The patient’s age and the reason for referral were also recorded.
Verbal consent was obtained from all patients before actual measurements. Ethical approval to conduct the study was obtained from the National Research Ethics Service (National Patient Safety Agency) and the local Research Governance Team.
Statistical analysis was carried out using Pearson correlation analysis and Student’s t test using SPSS (SPSS Inc., Chicago, IL, USA).
A total of 652 patients underwent genital size measurements during the study period, of whom 609 were eligible for analysis as Caucasian UK citizens. The mean age was 48 years (range 16–90 years). The mean values of penile dimensions recorded in the present study were pendulous length 8.7 cm (sd= 1.56 cm, 95% CI 0.12 cm), penopubic length 10.2 cm (sd 1.4 cm, 95% CI 0.11 cm) and stretched length 14.3 cm (sd 1.68 cm, 95% CI 0.13 cm). The cohort results are displayed as a nomogram in Fig. 1 and as distribution curves for pendulous and stretched flaccid lengths in Figs 2 and 3. The mean testicular volume was 19.8 mL (sd 5.4 mL) for both testicles (right 19.8 mL, left 19.8 mL).
Using Pearson correlation analysis there was no significant difference in penile length between men of differing ages (Fig. 4). There was also no correlation between penile length and testicular volume (Table 2).
Table 2. Penile length (cm, mean ±sd) and testicular volume
Penopubic length (cm)
Stretched length (cm)
Men presenting with penile disease (including phimosis, Peyronie’s disease) had slightly shorter penile length (pendulous −3.3 mm, P= 0.014; penopubic −2.3 mm, P= 0.029; stretched −5.1 mm, P < 0.001) compared with the other referral groups (erectile dysfunction, testicular disease, prostate and bladder disease) as shown in Table 3. There were no differences between the other referral groups.
Outpatient clinic measurements (n= 499) showed averages of 8.6 cm pendulous (sd 1.5 cm +/−), 10.2 cm penopubic (sd 1.4 cm +/−) and 14.3 cm stretched flaccid lengths (sd 1.5 cm +/−) compared with theatre measurements (n= 115, includes four patients with both measures) of 8.9 cm (sd 1.6 cm +/−), 10.4 cm (sd 1.5 cm +/−) and 14.7 cm (sd 2.1 cm +/−), respectively. Student’s t-test showed significant differences for longer length measurements in theatre for pendulous (3 mm, P= 0.16) and stretched flaccid (4 mm, P= 0.02) lengths, but not for penopubic length (2 mm, P= 0.03).
According to the definition of micropenis as a penile length below 2.5 standard deviations of the mean , a micropenis in our cohort would be defined as less than 4.7 cm pendulous, 6.7 cm penopubic and 10.1 cm stretched flaccid length.
This study describes one of the largest cohorts of men undergoing penile size measurements in Europe and the largest UK study (see Table 1). The range of measurements collected in this study will be of great use to clinicians treating men with concerns over penile length, as well as helping to diagnose patients with true micropenis.
The data were collected prospectively. We did not measure flaccid penile circumference, which might have been of additional interest. Nor did we collect data on erect penile length, because this would have required more invasive investigations and additional costs.
Our study was conducted by a single investigator (RD) with only a small data contribution (5%) from a second investigator (BS) and we did not assess interobserver differences. Another limitation of this study is that we did not assess possible test/repeat test variations.
Although patient selection may have contributed to the length differences between the outpatient patient group and the theatre patient group, it seems more likely that measurements taken under general anaesthesia were taken with slightly more force applied during the measuring process, resulting in marginally longer average measurements. Although significant, the differences only amounted to a few millimetres.
Lastly, we accept that the Prader Orchidometer may underestimate testicular volumes, especially in individuals with testicular volume exceeding 25 mL. However, the numbers of patients falling into this category were small in our study (n= 29 right testis, n= 30 left testis) and the overall impact is likely to be minimal.
The data show an average flaccid pendulous length of 8.7 cm, which may serve as a reference value for ‘shower room appearance’ and a stretched flaccid length of 14.3 cm as ‘comparative medical standard’ for the Caucasian UK citizen. The length of the stretched flaccid penis may be more difficult to measure, compared with the pendulous penis, particularly in patients with morbid obesity or phimosis. It is, however. a better measurement to estimate the true length of the penis, as the pendulous penile length may be shortened by a prominent prepubic fat pad, which buries part of the corpora cavernosa. Our study also suggests that average penile length does not generally decrease with age, although we are aware of the occasional individual patient in the outpatient clinic who does complain of losing penile length.
It is not surprising that men referred with penile disease had a marginally shorter penile length as this referral group included many men with Peyronie’s disease and those with a micropenis. No differences in penile length were found in patients with erectile dysfunction and those with potentially malfunctioning testes (undescended/absent testis, varicocele, infertility).
The correlation between stretched flaccid and erect penile lengths needs further clarification. Some studies have suggested that stretched flaccid length approximates to erect penile length [3,5,13], whereas others reported that erectile length exceeded stretched flaccid length significantly by a mean of 1–3.75 cm [7,9,16]. In any case, stretched flaccid penile length is thought to correlate better with erect penile length than with flaccid penile length alone [5,9].
According to our data the penile length threshold for a micropenis for UK men is 4.7 cm pendulous length, 6.7 cm penopubic length and 10.1 cm stretched flaccid length (average length minus 2.5 sd) . It has been arbitrarily suggested that any adult penis with a stretched flaccid or erect length of less than 7.5 cm is a true micropenis . The real question must be about the minimum length of the erect adult penis below which penetration in ordinary sexual positions becomes difficult or impossible. In our opinion an erect length below 10 cm may well cause functional problems.
Table 1 shows previously published worldwide data on penile length, including the data presented in this study. The differences suggest regional and therefore likely racial differences in penile length. However, there is no standardization of penile measurement technique, which would allow direct comparison of the data. Mondaini et al.  designed a penile length nomogram, which is applicable for young Italian men. We hope that the detailed description of our measurement technique enables others to achieve similar measurements by using the same technique.
We believe that the development of a national reference range may help in treating three patient groups. First, normal men with concerns about their genital size. Sexual literature available to men in modern Western society may raise wrong expectations and perceptions of normal sexual performance and genital size. Adolescents and adult men may feel insecure about their own adequacy. These patients can usually be reassured by sharing the relevant medical knowledge with them [2,14]. Second, patients with penile dysmorphophobia. It is important to identify these patients, who have concerns about their penile size despite a normally sized penis. These patients fail to be reassured as regards their normal penile size because their underlying problem is psychological. Such patients should be offered psychiatric help before considering any surgery for them. Penile lengthening surgery for dysmorphophobic patients is controversial and patient satisfaction after surgery is low . Finally, the reference range will help to identify patients with a true micropenis. A micropenis is defined as a normally formed penis that is at least 2.5 standard deviations below the mean in size . A micropenis can be the result of hypogonadotrophic hypogonadism, primary hypogonadism, androgen insensitivity or it can be idiopathic. It may be associated with Klinefelter syndrome and several other rare syndromes (e.g. Kallmann, Prader–Willi, Lawrence–Moon–Biedl) . Patients identified in paediatric practice and treated adequately with hormonal support have a 70% chance of reaching normal adult penile length (within 1 sd) . Unfortunately treatment options for the adult micropenis are limited. Various penile augmentation techniques have been described [21,22], which either do not provide true elongation of the corpora cavernosa or involve extensive penile surgery with disassembly or implant and are not established routine techniques [23,24]. Additionally there is limited evidence of the efficacy of mechanical lengthening treatments by penile extenders, but not by vacuum pump devices . Despite these limitations, patients with true micropenis may warrant attempts at surgical treatment; additionally, they may benefit from additional psychological counselling. In our patient group all symptomatic men with a micropenis were offered counselling and two subsequently underwent surgery by suspensory ligament division and prepubic fat excision, respectively.
Concern over penile size is not uncommon. The results of this study help to establish a reference range for male genital size in the UK, which should be helpful for urologists in counselling patients.
We would like to thank Mr Grant Stewart, Clinical Lecturer in Urological Surgery and Honorary Specialist Registrar at the Western General Hospital, Edinburgh for his valuable critical scientific review of this article before submission.