WE'RE often told not to judge a book by its cover.
But according to a new study, some people really do judge personality based on penis size.
While those with a smaller pecker are seen as more neurotic and boring.
Scientists already believe humans make judgments on personality based off faces and dress-sense - and now these experts think the same is true of penises.
"Genital appearance may contribute to socially shared implicit theories about people, regardless if these impressions reflect the true personality of the person being assessed," authors said.
The study, published in the journal of Sexuality & Culture, looked at what assumptions people came to of a person, based on a picture of just their penis.
The team showed 106 people, most of whom were women (80 per cent), photos of 24 penises that varied in girth, length and amount of pubic hair.
After looking at the image, each participant was then asked to respond to several questions including whether the owner was kind, extroverted, sexually active and attractive.
Those with longer and girthier penises were considered to be more attractive, more open and generally nicer.
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And men with trimmed pubic hair were seen as more conscientious then those with lots of untamed hair.
Shorter and narrower penises, on the other hand, were perceived as more neurotic and less open to new experiences.
Overall, the findings suggest that impressions can be formed of men based purely on their penises.
"While previous studies found that penises slightly above average were perceived as ideal, the present study found that penises with larger girth and length were perceived as prototypical," authors added.
The scientists found it surprising how many men left their pubic hair untrimmed despite the fact most women perceived penises with ungroomed pubic hair very negatively.
"While much more work must be conducted to understand the social pressure men face to groom their pubic hair, the significantly low rating for penises with untrimmed pubic hair in the domains of extraversion, conscientiousness, agreeableness, and openness was noteworthy," they explained.
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The authors said they hoped to conduct further research into whether assumptions of personality based on penis size are accurate.
Previous research suggests the average flaccid penis length is 3.6 inches.
The average length of an erect penis stands at 5.16 inches.
There is a small correlation between the length and the person's height.
An earlier study from Target Map found Britain's average erect schlong is from 3.5-5.8 inches.
This may be because they asked 1,000 blokes to reveal their own size back in 2020 (which could have led to a few extra inches being added).
They found the average penis length in the UK is 6.36 inches.