I think it was ElectroBOOM video that taught me counting to 31 on one hand, which means both are 1,023 maximum.

10 fingers, each holding one value.
Example:

Finger	Value
Left thumb	1
Left index	2
Left middle	4
Left ring	8
Left pinkie	16
Right pinkie	32
Right ring	64
Right middle	128
Right index	256
Right thumb	512

Together up to 1,023.