4256 px by 7120 px with 7 layers
So (4256 * 7120 * 4) * (7 + 2) = 1,090,897,920 bits.
Roughly 1 GB of RAM, just for Paint.NET.
Edit: It's a Giga bit, not byte.
Actually, Bob, that original formula is referring to Bytes, not bits.
(4,256 * 7,120 * 4) * (7 + 2) = 1,090,897,920 Bytes