Seed potato size

This spring i planted 22-24/kg size and got about 6-7kg(planted in 2 batches with about 2 weeks difference and on different soil) out of each kilo. Job done chemical-free. This is not the top rate, but for  my plot is not bad 
 Main problem - here more common big size potato seeds, well, local supplier forcing me to buy 8-10/kg size and cut them    and "magic powder" to protect cuts, which is not free 
Hopefully i can get needed amount from place, where i bought seeds in the spring. Next step is to get my own seeds in 24-28/kg size and use lots of compost to improve soil.
Oh, i will be appreciated to collect some statistics
1)size of seeds number/kg
2)outcome kg per kilo seeds(count any size, which you took from field)

Thanks in advance