MEN worry more about what their mates think, rather than their partner, when it comes to stature and the size of their penis.

It's a phenomenon called the "locker room syndrome", says Doctor of Clinical Psychology student Annabel Chan, who obtained penis measurements from more than 500 men worldwide.

The men also answered questions designed to probe the link between penis size, male body image and mental health, says Ms Chan who is a PhD student at Melbourne's Victoria University.

"It's the locker room syndrome," Ms Chan says.

"That's when they feel they should be bigger whereas when they are on their own they are actually quite happy with themselves."

The men, aged 18 to 76, were asked to indicate their ideal body size and then compare this to what they believed other men would nominate.

A majority (65 per cent) said their ideal male body size would be smaller than the ideal size suggested by others.

The men were also asked whether they believed they would be a better sexual partner if they had a bigger penis.

Ms Chan says the men were "more concerned about how their overall body-size compared to the perceived male ideal than they are about how their size might impact on their sexual relations".

The survey, which was completed online, asked men to measure their erect penises.

Ms Chan says she expected to receive some overstated measurements but the self-reported data fell within the normal range of about 10 to 15cm.

"I thought people would report themselves as being very big, but they have been quite average," she says.

Marrying up penis length data with responses to questions about perception, health and lifestyle revealed:

MEN with larger than average penises also reported higher levels of self-esteem, better general health and higher overall body satisfaction.

MEN who were happy with the size of their penis were also less likely to have used an online dating service, or to have used viagra.

OVERWEIGHT men had lower self-esteem, higher body dissatisfaction and greater use of the internet for socialising.

"We have relatively little data about the body image of men because most of the research in this area concentrates on women," Ms Chan says.

"It means men don't really get much help in terms of therapy, and options out there to get help."