Eric Keller wrote:

My first post to this group so please forgive me if this has been
asked and answered.

I plan on burying my downspouts and having them merge into one 4"
drain pipe. The discharge will be at a nice point far from my house.
The length will be about 200 ft from the first downspout to the
discharge. There will be a total of 4 downspouts merging into the same
line.

My question is: How many downspouts can I run into a single 4" PVC
pipe within the 200 ft length? I live near Chicago and we get plenty
of rain.

And ice. I suspect a 4" pipe will freeze up a week after the first
snow and not thaw until April.

IMO- you need to go either with at least a 8" pipe or use shallow
ditches to prevent freezing. The number of downspouts doesn't
matter-- the surface area that you're draining does.

I've got a 12" culvert that takes the water from one side of a 2-car
garage. It has a smooth bottom is well pitched and is on the south
side of the garage-- but it gets 1/2 full of ice sometimes. I'm
glad I didn't use 6" pipe.

Jim