The question of what's a normal sized penis now has a well-informed answer.

Doctors searched through 17 published studies on more than 15,000 men who had their penis size measured by a health professional and graphed the averages in Tuesday's issue of BJU International, formerly the British Journal of Urology.

The graphs will help doctors reassure the large majority of men that their penis size is in the normal range, said study author Dr. David Veale, of King's College London.

For men with small penis anxiety, education and counselling may be helpful, Veale and his team said.

"It is a hidden problem," Veale said in an email. "Men are more likely to seek solutions on the internet with lotions, potions, extenders or surgery."

Dr. Debbie Sookman is the director of the Obsessive Compulsive Disorder (OCD) Clinic at McGill University Health Centre in Montreal.

"As clinicians and as experts helping an individual who may come with that concern, we should start with psychoeducation in terms of penises being all kinds of different sizes, differing across races and that it's the vast majority of men who come concerned are well within the normal range," said Sookman, who is also a psychiatry professor at McGill and president of the Canadian Institute for Obsessive Compulsive Disorders.

"Is the concern restricted only to this one body part, or is there any evidence the man is presenting with what we call body dysmorphic disorder?"

Some men who are preoccupied and severely distressed with the size or shape of their penis may be diagnosed with body dysmorphic disorder, one of Veale's specialities.

Men with body dysmorphic disorder may spend a lot of time checking the internet and having intrusive thoughts that cause distress and avoidance, Sookman said.

Evidence-based treatments for body dysmorphic disorder includes psychoeducation, cognitive therapy, skills to face fears as well as the development of resilience and strategies to improve self-esteem.

The researchers say measuring penis size is important in assessing men who complain of a small penis and to investigate the relationship between condom failure and penile dimensions.

The average measurements were:

Flaccid length 9.16 cm (3.61 in.)

Flaccid stretched length 13.24 cm (5.21 in.)

Erect length 13.12 cm (5.17 in.)

Flaccid girth or circumference 9.31 cm (3.67 in.)

Erect circumference 11.66 cm (4.59 in.)

Stretched flaccid length looks to be an excellent estimate of erect penile length, they said.

The reviewers recommended taking the measurements in a private, air-conditioned consulting room using a disposable tape measure.

Flaccid circumference is measured mid-shaft, length is skin to tip and bone to tip.

One of the limitations is relatively few erect measurements have been clinically done. Study volunteers may also have been more confident in their penis size than the general male population.

In 2006, the reviewers noted a large internet survey of heterosexual men and women suggested 85 per cent of women were satisfied with their partner's penis size and 55 per cent of men were satisfied with their own size. The preferences may differ in the homosexual community, the researchers said.