"Size difference" refers to the variation or contrast in size between two or more things. It highlights the discrepancy or disparity in their physical dimensions or magnitudes. Full definition
Because of size differences between the vehicles, motorcycle accidents can result in serious head injury, paralysis, catastrophic injuries or death. (monseesmayer.com)
M: That's right, although it gets complicated because the bigger a species is, the more likely you'll get some degree of size difference between males and females. (discovermagazine.com)
The available data suggests that the differences are biologically predetermined and largely due to size differences in contracting muscles. (shapesense.com)