Purpose: We provide guidelines of penile length and circumference to assist in counseling patients considering penile augmentation.

Materials and Methods: We prospectively measured flaccid and erect penile dimensions in 80 physically normal men before and after pharmacological erection.

Results: Mean flaccid length was 8.8 cm., stretched length 12.4 cm. and erect length 12.9 cm. Neither patient age nor size of the flaccid penis accurately predicted erectile length. Stretched length most closely correlated with erect length.

Conclusions: Only men with a flaccid length of less than 4 cm., or a stretched or erect length of less than 7.5 cm. should be considered candidates for penile lengthening.

Patients and Methods

We performed a prospective study of flaccid and erect penile dimensions in 80 physically normal men at our institution. All patients were evaluated for sexual dysfunction but had no congenital or acquired abnormalities of the penis. Patients were excluded if they had a history of Peyronie's disease, radical prostatectomy, urethroplasty or other penile surgery (except circumcision). Patient age and race were recorded.

Tape measurements of the flaccid and erect penis were obtained to the nearest 0.5 cm. by 1 examiner. Flaccif length, circumference, depth of the prepubic fat pad and stretched penile length Figure 1 were measured immediately after the patient undressed to minimize the effects of temperature. Measurements were made of the length from the pub-penile skin junction to the meatus, circumference at the mid shaft and fat pad depth by pushing the tape into the pubic bone. Stretched flaccid length was measured from the pub-penile skin junction to the meatus under maximal extension of the phallus. All patients underwent intracavernous injection of prostaglandin E1 for evaluation of erectile dysfunction. After a period of privacy and self-stimulation, penile length and circumference were measured at full erection. If full rigidity was not obtained a mixture of phentolamine, papaverine and prostaglandin E1 was injected to enhance erection, and measurements were repeated. Confidentiality was maintained in accordance with criteria of the committee on human research at our university.

图1. Penile length:阴茎耻骨前皮肤至尿道口的长度，即阴茎长度。Fat depth:阴茎根部耻骨前皮下脂肪的厚度。

Statistical analysis was performed with analysis of variance for comparison of continuous and categorical variables. The level of significance was chosen as p = 0.05. To determine the relationship among penile dimensions in different states, regression plots and coefficient of determination (R²) calculations were used.

Results

The descriptive statistics for all 80 subjects (mean plus or minus standard deviation) are listed in Table 1. Distribution of patient age was biphasic, with a peak in the third decade and 1 in the sixth decade.

平均疲软长度（Mean flaccid length）为8.85 cm， 平均勃起长度（ mean erect length）为 12.89 cm.两者之差为勃起增加的长度平均 4.04 cm.. 功能长度（Functional penile length）为勃起长度与耻骨前皮下脂肪厚度之和。阴茎体积（ Phallic volume）通过计算机软件算出。. 54名白人  (67.5 percent) , 16名 (20 percent) 黑人 ， 10名 (12.5 percent) 亚洲人.

The regression plot of flaccid and erect lengths (R² = 0.678) is shown in Figure 2,(A). However, stretched flaccid length more closely predicted erect length (R² = 0.793), as shown in the regression plot in Figure 2,(B). Fat pad depth did not correlate with any parameter of penile size. Penile volume increased an average of 40 cc with erection, consistent with reports of the volume of blood necessary for erection. [8,9]

[Help with image viewing]

Figure 2. A, correlation between flaccid and erect lengths (R2 = 0.678). B, correlation between stretched flaccid and erect lengths (R2 = 0.793)

勃起长度的增加与疲软长度没有可以预期的相关性(R² = 0.0001, Figure 3). 当阴茎较短 (9.5 cm. 或更小 ) 或较长  (10 cm或更长)，其勃起长度的增加没有显著差异(前者平均增加 3.98， 后者增加 4.06 cm., p = 0.8274).

Subjects were stratified by age as 40 years old or younger and older than 40 years to study the effect of age on fat pad depth, flaccid length, stretched length and erectile length increase Table 2. Only fat pad depth differed significantly (p = 0.0068), being greater in the older subjects.

表2:阴茎与年龄的关系。

Table 2. Mean penile dimensions according to patient age

Discussion

Our results define mean length and circumference of the flaccid and erect penis, which may be useful when counseling patients considering penile lengthening or girth enhancement. Flaccid and erect dimensions are important, since patient perception of small size in either state may be a motivating factor. Our data confirm the close correlation between stretched and erect lengths noted by Schonfeld and Beebe, [3] making measurement of stretched length a suitable estimate of erect length.

We consider normal penile dimensions to be any length within 2 standard deviations of the mean. Therefore, we recommend penile augmentation only in the interested patient with a flaccid length of less than 4 cm. or a stretched length of less than 7.5 cm. These guidelines are different from those proposed for micropenis, in which a stretched length of 9.3 cm. in an adult is considered inadequate. Our population is older with greater variation in penile length and extensibility, reflecting the older age of patients undergoing penile augmentation. [10] These guidelines should be applied only to the patient with significant concerns regarding phallic size and not as a general standard for all men. In our experience anxiety regarding phallic size has little relationship to true penile length.对阴茎大小的焦虑与阴茎的实际大小没有关系。随年龄增大，阴茎的伸缩性由于白膜弹性的损失而减小。

The dimensions obtained in our study differ from those of previous reports Table 3. [2,3,5-7] Variation in dimensions among studies may be due to differences in patient population or methodology. Age differences may explain some variation in length, since penile extensibility decreases with age due to loss of elasticity of the tunica albuginea. [6,11] Loeb, [2] and Schonfeld and Beebe [3] recorded phallic dimensions in younger populations, which may explain differences in flaccid and stretched penile lengths, although we found no statistically significant difference in these dimensions when comparing old and young patients Table 2.

[Help with image viewing]

Table 3. Studies of penile dimensions from 1899 to present

We obtained measurements in patients with erectile dysfunction. Corporeal fibrosis may decrease penile extensibility. However, de Goes et al found no correlation between penile extensibility and degree of smooth muscle fibrosis in the corpora cavernosa. [11] Loss of elasticity of the tunica albuginea may contribute to differences in penile extensibility but the relationship between tunical abnormalities and erectile dysfunction has not been well defined. [12,13]

Bondil et al reported significantly longer flaccid and stretched lengths than those in other studies Table 3. [6] Although these differences may represent a normal variation, the methodology of their study differed in several respects from other reports. Measurements were not obtained by 1 examiner, and stretched length was measured only after 3 repeated manual stretchings of the penis. The data of Kinsey et al, [14] analyzed by Jamison and Gebhard, [5] report the longest erect penile length. Despite the large sample size, the validity of these data must be assessed with the knowledge that all measurements were self-recorded and significant bias may preclude comparison with other studies.

The depth of the pubic fat pad may significantly alter the perception of penile length. An increase in fat pad depth will decrease the visible pendulous length of the penis. Many men complain of a retractile penis, and obesity contributes to this phenomenon. Knowledge of functional penile length, including that buried by the fat pad, may decrease anxiety, concerning erect size in certain men. Weight loss or suprapubic liposuction may represent less drastic alternatives to release of the suspensory ligament with its resultant complications.

Phallic circumference parallels penile length in the flaccid and erect states. The normal penile shaft is slightly narrower than the corona and we can find no indication to alter this relationship. Girth enhancement with fat injection can lead to an unpleasing change in penile appearance. [15]

Conclusions

To our knowledge our study of 80 subjects is the first to measure penile length in all states (flaccid, stretched and erect). Mean flaccid length was 8.8 cm., stretched length 12.4 cm. and erect length 12.8 cm. The correlation between flaccid and erect lengths is not sufficiently close to use flaccid length as the sole measure of penile size. However, stretched length does allow for an estimation of erect length to help counsel patients with concerns regarding penile adequacy. Only men with a flaccid length of less than 4 cm., or a stretched or erect length of less than 7.5 cm. should be considered candidates for penile lengthening. Guidelines for girth enhancement are not proposed because of the lack of an aesthetic rationale for this technique.

REFERENCES

1. Long, D. C.: Elongation of the penis. Chung Hua Cheng Hsing Shao Shang Wai Ko Tsa Chih, 6: 17, 1990. [Context Link]

2. Loeb, H.: Harnrohrencapacitat und Tripperspritzen. Munch. Med. Wochenschr., 46: 1016, 1899. [Context Link]

3. Schonfeld, W. A. and Beebe, G. W.: Normal growth and variation in the male genitalia from birth to maturity. J. Urol., 48: 759, 1942. [Context Link]

4. Masters, W. H. and Johnson, V. E.: Human Sexual Response. Boston: Little, Brown & Co., 1966. [Context Link]

5. Jamison, P. L. and Gebhard, P. H.: Penis size increase between flaccid and erect state: an analysis of the Kinsey data. J. Sex Res., 24: 177, 1988. [Context Link]

6. Bondil, P., Costa, P., Daures, J. P., Louis, J. F. and Navratil, H.: Clinical study of the longitudinal deformation of the flaccid penis and of its variations with aging. Eur. Urol., 21: 284, 1992. [Context Link]

7. da Ros, C., Teloken, C., Sogari, P., Barcelos, M., Silva, F., Souto, C. and Alegre, P.: Caucasian penis: what is the normal size? J. Urol., part 2, 151: 323A, abstract 381, 1994. [Context Link]

8. Chen, K. K., Chou, Y. H., Chang, L. S. and Chen, M. T.: Sonographic measurement of penile erectile volume. J. Clin. Ultrasound, 20: 247, 1992. [Context Link]

9. Nelson, R. P. and Lue, T. F.: Determination of erectile penile volume by ultrasonography. J. Urol., 141: 1123, 1989. Bibliographic Links [Context Link]

10. Feldman, K. W. and Smith, D. W.: Fetal phallic growth and penile standards for newborn male infants. J. Ped., 86: 395, 1975. Bibliographic Links [Context Link]

11. de Goes, P. M., Wespes, E. and Schulman, C.: Penile extensibility: to what is it related? J. Urol., 148: 1432, 1992. [Context Link]

12. Bitsch, M., Kromann-Andersen, B., Schou, J. and Sjontoft, E.: The elasticity and the tensile strength of the tunica albuginea of the corpora cavernosa. J. Urol., 143: 642, 1990. Bibliographic Links [Context Link]

13. Padma-Nathan, H., Cheung, D., Perelman, N., Boyd, S. D. and Nimni, M. E.: The effects of aging, diabetes and vascular ischemia on the biochemical composition of collagen found in the corpora and tunica of potent and impotent men. Int. J. Impotence Res., suppl. 2, 2: 75, 1990. [Context Link]

14. Kinsey, A. C., Pomeroy, W. B. and Martin, C. E.: Sexual Behavior in the Human Male. Philadelphia: W. B. Saunders Co., 1948. [Context Link]

15. Wessells, H., Lue, T. F. and McAninch, J. W.: Complications of penile lengthening and augmentation seen at 1 referral center. J. Urol., 155: 1617, 1996. [Context Link]