Roofing question - How many downspouts do I need for a given area of roof?

My roof (2 story, 1925 square foot house) was just replaced and I heard the project manager and crew chief debating whether I needed one or two downspouts for the bottom roof. On the front of the house, everything from the ridge forward drains toward the front. That includes a large dormer (2nd story), whose downspout drains directly onto the lower roof. Water from that flows down about 5 feet of 50 year asphalt composition shingles into the gutter on the lower roof where it meets the runoff from the lower roof. The debate was whether one or two downspouts are needed from the lower gutter and the project manager decided on one, at one side. I wonder if this is enough. I also wonder if there shouldn't be an extension of downspout from the dormer roof directly to the lower gutter so all that water doesn't run down one part of the lower roof for 5 feet.
The total area of roof forward of the ridge is something like 700 square feet and all that going down one downspout (standard size aluminum, I figure around 7 square inch cross section) seems like a lot to expect of one downspout in a heavy rain. What is the situation? Is there a website I can go to to figure out downspout requirements for a given roof area? Thanks for any help.
Dan
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I found some sites that allow you to calculate downspout/gutter requirements.
This is one of the best:
http://www.copper.org/applications/architecture/arch_dhb/gutters_downspouts/intro.html
This Google search came up with several good sites:
http://www.google.com/search?sourceid=navclient&ie=UTF-8&rls=GGLD,GGLD:2004-38,GGLD:en&q signing+a+gutter+and+downspout+system
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