Well, it would depend on when you're wanting to talk about. Early line battles would last no more than a day and have no more than eighty to a hundred thousand people involved, minimal artillery (say no more than fifty or so guns per army) and minimal cavalry on the flanks. Warfare was limited due to a turn toward professional armies and because of the cost of these professional armies. So the need to use larger armies is not common.

However, the French Revolution let the genie of Nationalism out of the bottle (and the genie of mass conscription), armies became far larger. Battles during the French Revolution started small (with thirty or forty thousand men on each side) but once Napoleon came to power and started creating the Corps system meant to allow greater flexibility and movement, battles were able to become much larger. At Austerlitz, Napoleon's sixty seven thousand French (with no more than a hundred guns) faced almost ninety thousand Austrians and Russians with roughly the same amount of artillery. The Allied forces lost sixteen thousand while the French lost about half of that (and that is dead and wounded), so causalities were never horrendous as you might see in modern combat/post-Napoleonic warfare.

But this trend wouldn't stop, the genie was out of the battle and it would eventually grow to a quarter of a million French (plus allies) with about six hundred guns against four hundred thousand Allies with thirteen hundred guns during the Battle of Leipzig in 1813. So in eight years, armies tripled. About thirty four thousand French (with allies) died or were wounded while the Allies had fifty four thousand were killed or wounded.