For each full regiment of infantry and cavalry of 1, 000 men, 6 wagons for baggage, camp equipage, &c.

The supply train for forage, subsistence, quartermaster's stores, &c., to each 1, 000 men, cavalry and infantry, 7 wagons.

to every 1, 000 men, cavalry and infantry, for small-arms ammunition, 4 wagons.

To each 1, 500 men, cavalry and infantry, for hospital supplies, 3 wagons. [Figure 2 per 1,000 man regiment]

Total 20 for a 1,000 man regiment
http://ehistory.osu.edu/osu/sources/recordView.cfm?Content=045/0653

See also: http://history-sites.com/cgi-bin/boards/txcwmb/index.cgi?noframes;read=9951

Other considerations:

Army of the Potomac regulations

The regulation load of a four-horse team on good roads was 2,800 pounds. For a six-mule team on a macadamized road, it was 4,000-4,500 pounds; on a solid dirt road, 3,000-3,500 pounds; and on a dirt track in rough country, 1,800-2,500 pounds, plus in all cases, five to ten days' grain for themselves. On good road the regulation speed was two and one-half miles per hour.
"The American Civil War and the Origins of Modern Warfare, Ideas, Organization, and Field Command," Indiana University Press, 1988/1992, p. 45