A world-first study has revealed that the vast majority of men’s penises grow by less than 4cm when erect.

The research, by scientists at the University of California, Irvine, studied 274 men and found that 74 per cent were ‘showers’ and had penises that grow by 4cm (1.57inches) or less when aroused.

The remaining 26 per cent, called ‘growers’ by the researchers, enlarged by an average of 5.3cm (2.08inches).

Growers in the study had an average erection length of 15.5cm (6.1inches), whereas showers’ were 13.1cm (5.15 inches).


Men over 55 are significantly more likely to be showers, the research adds.

This may be due to older males having higher levels of inflammation in their bodies that reduces blood flow and tissue elasticity, preventing their penises from growing when they are turned on, according to the researchers.

The scientists hope their findings will help men who have prosthetic penises fitted to be more aware of how their members may grow when erect.

Previous studies suggest men with larger penises are more body confident, however, separate findings also imply a male’s genital size does not influence a woman’s sexual satisfaction.

Despite this, research has shown women find men more attractive if they have large sexual organs.

Scientists have revealed how a woman can tell if her man is a grower or a shower (stock)
Scientists have revealed how a woman can tell if her man is a grower or a shower (stock)

How the research was carried out 

The researchers analysed 274 men who were tested for erectile dysfunction back in 2011-to-2013.

The length of the men’s penises were measured in a flaccid state.

These measurements were then repeated after the males were injected at the base of their genitals with a substance that causes blood vessels to expand, while they were exposed to ‘audiovisual sexual simulation’.

Growers enlarge by 5.3cm, showers by 3.1cm 

Results suggest that growers tend to increase by 5.3cm when aroused compared to 3.1cm in showers.

Race or relationship status does not influence how much men’s penises change when erect.

Whether males are smokers or have diabetes also does not affect their genital enlargement, which contradicts previous findings.

Smaller flaccid penises actually lead to bigger erections

And the size of a man’s flaccid penis does not affect whether he is more likely to be a grower or a shower.

In fact, growers – whose penises are smaller when not erect – are likely to have a larger erection than someone whose penis is longer than theirs when flaccid.

Growers in the study had an average erection length of 15.5cm, whereas showers’ were 13.1cm.

Both men and women thought to prefer larger appendages 

Although the researchers said men put ‘undue focus and attention’ on the size of their penis, both sexes are happier with a larger member.

They wrote: ‘Research documents that men with larger penises have better body image, genital satisfaction, and higher feelings of sexual competence.’

Adding: ‘Multiple studies aimed at assessing female preference with regard to penis size have reported that a larger penis increases male attractiveness and female perceptions of sexual satisfaction.’

The findings were published in the International Journal of Impotence Research.

Soaring temperatures are giving men ‘summer penises’ 

This comes after males claimed last month the heatwave is giving them ‘summer penises’.

One man asked users of an online forum if anyone else’s genitals grow during the summer months.

Click on this link to read more