Data from the Australian study shown here confirm earlier research: on average, the hand spans of adult male (thumb to fifth finger) are about one inch (or 2.5 centimetres) greater than those of adult females. This means men can reach, on average, more than one extra white key on the current keyboard.
The chart below illustrates the marked gender difference in 1-5 spans. From this study, the mean 1-5 span for males is 8.9 inches (22.6 cm) and for females, 7.9 inches (20.1 cm), a difference which is statistically significant at the 5% level. The taller peak on the left reflects the higher proportion of female pianists in the sample; the male to female ratio was about 2:1.
One can also see that only a very small proportion of males (2% in this study) have a span less than the female average, and that a similarly small proportion of females (2.9%) have a span larger than the male average. The tables underneath provide some basic summary measures for both 1-5 and 2-5 spans. The gender difference of approximately 0.5 inches in 2-5 spans is also statistically significant.