Hi, I don't grow veg, but years ago the recommended size for seed potatoes was about the size of a large hens egg, you would probably get more information if you search Solanum tuberosum online, Derek.

Thank you

Why only 10? Are you going to grow in bags or in the ground and if bags then how many? Are they earlies or maincrop. As Derek says, the books say the size of a large hen's egg. If they are earlies and are going to grow in bags, it doesn't matter if you put 4 or even 5 in a bag. Yes, they might give a crop of smaller potatoes but I find they are more desirable early in the season.

Cheers
In bags & I only have room for 10 which whould be best & There main crop.

The main crop varieties will be the most vigorous and will be so cheap and plentiful in the shops by the time they mature. In future I would go for the early varieties which are greatly appreciated coming straight from your garden to the dinner plate when they are also at a premium price in the shops.