Basing for 6mm figures
We use 6mm figures and the 1 inch to 100 yards ground scale. A normal sized infantry battalion is on a 50mm frontage by 30mm depth mdf base. Roughly 10 figures to a rank, 3 ranks to a battalion. Gives a nice impression. Smaller battalions are based on 40mm by 30mm bases (about 24 figures). Not done any large battalions yet but they would be on a 60mm by 30mm base and have more figures(probably 36ish). Cavalry squadron groups are also based on a 40mm by 30mm base - two ranks, 5 figures per rank.
Command stands are based on circular bases. Obviously increasing in size and the number of figures as you progress up the hierarchy.
1 inch to 100 yards makes it much easier to convert maps etc...
I'm using 6mm H&R figures on 30mm x 20mm bases. Putting 3 ranks of 8 each for infantry or 1 rank of 5 cavalry. Here's a overhead view of my Prussian Guard Brigade circa 1813. I'm playing at the 1/150 scale.