What do you consider a standard loaf pan? 8x4 or 9x5?

I would say 9 x 5. The difference is 9 x 5 holds 8 cups, 8 x 5 holds 6 cups. Unless stated go for the larger pan. BB

I’ve used both and either will work just fine and will fit without overflowing! I consider 9x5 standard but if you want a larger loaf, use the smaller pan.