I tried growing potatoes in a sack at home for the first time this year. Just one sack and three Winston potatoes. All I got was 8 potatoes - but 8 big potatoes. They crop weighed in at over 3Kg and the largest potato was 686 grams (over a pound and a half).
We only needed one for a meal for two. Next year I might not leave it so long before tipping them out. 2017 is proving to be the year of the massive tattie!
How to Dig Potatoes