Flaccid length
One study found the mean flaccid penis length to be 3.5 inches (8.9 cm) (measured by staff).[5] A review of several studies have shown average flaccid length to be 9–10 cm.[12] Length of the flaccid penis does not necessarily correspond to length of the erect penis; some smaller flaccid penises can grow much larger, and some larger flaccid penises cannot grow much larger.[16][17]

The penis and scrotum can contract involuntarily in reaction to cold temperatures or nervousness, referred to by the slang term "shrinkage", due to action by the cremaster muscle. The same issue affects cyclist and exercise bike users, with prolonged pressure on the perineum from the saddle, and the straining of the exercise causing the penis and scrotum to contract involuntarily which is sometimes referred to as "gym balls" or "saddle balls". An incorrect saddle may ultimately cause erectile dysfunction (see crotch pressure for more information).

Penises that are short when flaccid but substantially larger when erect are colloquially known as "growers", while those with greater flaccid lengths that increase little when erect are known as "showers".

Flaccid penis length is a poor estimate of erect length, a better estimate is stretched length, that is 12–13 cm, as shown in review by Wylie and Erdley.[12]