Researchers from the University of New Mexico and the University of California studied 75 women aged 18 to 65.
Scientists presented them with 33 different 3D-printed plastic penises of various sizes, which were all blue-coloured and odourless to prevent any bias.
Researchers then asked the women which model was closest to their preferred penis size in a long-term partner, and then which penis model would be best for a one-time thing.
The women, on average, chose a penis of around 6.3in in length and 4.8in around for a long-term partner.
When it came to a one-night stand, however, the average plastic penis was a bit bigger – more like 6.4in long and 5in around.
Both of these penises were on the larger end of the spectrum. The average erect penis is 5.2in long and 4.6in in circumference, according to a study last year that looked at 15,000 penises worldwide.
Dr Nicole Prause, a sexual psychophysiologist, also asked the women about their previous sexual experiences with penises of all sizes.
Some 7% of women said they had ended a relationship because their partner’s penis had been ‘too large’.
However, significantly more women – 20% – admitted to dumping a guy because his penis was ‘too small’.