The same phenomenon affects cyclists and exercise bike users, with prolonged pressure on the perineum from the bicycle saddle and the straining of the exercise causing the penis and scrotum to contract involuntarily. An incorrect saddle may ultimately cause erectile dysfunction (see crotch pressure for more information). Individuals with hard flaccid syndrome or other pelvic floor disorders may temporarily have an abnormally small penis. Stretched
Neither age nor size of the flaccid penis accurately predicted erectile length. Stretched length has correlated with erect length in some cases. However, studies have also shown drastic differences between stretched and erect length. One study found that a minimal tension force of approximately 450 g during stretching of the penis was required to reach a full potential erection length. this study also found that tension forces exerted in this study by the urologist were shown to be significantly (P<0.01) lower than 450g. This may account for differences between stretched and erect length. The 2015 study of 15,521 men found that the average length of a stretched flaccid penis was 13.24 cm (5.21 inches) long, which is near identical to the average length of an erect human penis which is 13.12 cm (5.17 inches) long. An 2001 study of about 3,300 men published in European Urology concluded that flaccid stretched length was measured on average to about 12.5 cm (4.9 in). In addition, they checked for correlations in a random subset of the sample consisting of 325 men.
A 2020 review in the Journal of Sex & Marital Therapy found that the majority of men believed that the average erect penis length is more than 15.24 cm (6 inches). This inaccurate belief has likely been fed by inaccurate and exaggerated data presented in studies where the size of the participants erect  penis is self-reported. Participants may report overestimates of the size of their penis in the belief that a larger penis is more socially desirable. The same review analyzed the results from ten prior studies where measurements of erect penis size were made by researchers. They reported an erect penis to be between 12.95 and 13.92 cm (5.1 and 5.5 inches, respectively) in length, a result significantly below the average obtained in self-reported studies. The authors commented that results of such measurement studies may still be inflated due to volunteer bias – the possibility that men with larger penises may be more likely to choose to participate in such studies. Erect circumference
Similar results exist regarding studies of the circumference of the adult fully erect penis, with the measurement usually taken mid-shaft. As with length, studies that relied on self-measurement consistently reported a significantly higher average than those with staff measuring. In a study of penis size where measurements were taken in a laboratory setting, the average penis circumference when erect was 11.66 cm (4.59 inches).