According to my research, it is generally relatively difficult to make an exact statement, as "small" is a relative size specification and personal taste also plays a role. According to the manufacturer, the dimensions of the mouse are as follows:
MX Master 3S Mouse: Height: 124.9 mm; Width: 84.3 mm; Depth: 51 mm; Weight: 141 g
The dimensions may help you to get an idea of whether the size might fit.