450 based on desired yield. And yes, I am cutting them. The only problem was that I spent 10 dollars for ten seed potatoes, and only two of them were big enough to cut. (Much smaller then eggs, and with only a couple of sprouts per potato.) And that was without shipping, since I got them at a
local garden center. Prices online seemed to be about that much, too.
I bought some store potatoes and cut them up; 10 dollars for enough potatoes to plant 80 pieces. So 80 versus 12. The store potatoes I bought were organic, and healthy looking; they had already started to sprout. Even if only half of them grow, I would still be coming out ahead.
And given my luck, I would buy the expensive seed, and then get a disease anyway, and have wasted lots of money. At least this way there will be no great loss. Maybe in future years where I am very experienced in growing potatoes, and are depending on them more, I might buy certified seed.