I believe there is about 7,000 grains per pound- never measured it out myself and don’t plan to. Do the math for how many rounds that will give you depending on your load.
In my opinion, with the hazmat charge you need to order the 8lb cans to make it worth your while, and try to order with 1 or 2 buddies if possible.
powder and primers are one of the few things that I will actually go to gunshows for. assuming that you can find a vendor that has what you want, the admission fee is usually half what the hazmat fee is.
sometimes you can find a vendor online that will be at the show and place an order for pickup. that’s worked for me a couple of times. the biggest problem I have is getting them to sell me a respectable number of primers. These days they usually stick to 1 sleeve per customer.
otherwise, make one big honking order, putting in as much stuff as you can ride on one hazmat fee. primers and powder together usually gets you there, but you can get three sleeves of primers in one box. if you order too much you might get dinged for multiple boxes/hazmat fees.
OP, It’s best to find like minded hand loaders and get in to a group buy. 100 lbs of powder will give significant discounts. Usually this occurs at gun/skeet clubs. Bullets are done the same way.
That would be like counting how many inches are on a football field to prove the field is truly 100 yards. There’s nothing subjective about 1 lb equaling 7000 grains.