Two years ago we got 24 lbs of Yukon Gold and 30 lbs of Red Pontiacs from two 11' rows, 1.5 lbs of seed potatoes each. I like to use small seed potatoes that don't need cutting up. One less possible problem.
Last year was a total bust as we had gobs of rain, the potatoes were in a different location that got some standing water and they all rotted. Never came up.
This year we planted one 18' row in a raised bed using about 8 small seed potatoes each of Yukon Gold and Kennebec. We ended up with 18 lbs of Yukons and 15 lbs of Kennebec. No more planting potatoes in the raised bed as once they were hilled the first time there was hardly any soil to hill them the second time.
Doing a "by foot" comparison, that works out to about 2.5 lbs per row foot in 2018 and 1.8 lbs per row foot this year in a raised bed.