If you get a tin of new pots it should tell you what the drained weight is. You could work it out from there but it would really depend on the size of each spud. Invest in kitchen scales, you will find them very useful
Hi Angelina, Just to let you know that on the slimming world web site they have a feature that shows you what the diffrent weights look like, its cool, 28g cheddar for instance is about the same size as a small match box, and a HE B baked potatoe's about the size of a computers mouse, check it out, well worth it.