After yet again under estimating how many potatoes I need for mash does anyone have any tips for getting it right please?

[JustFabulous]

Preferably ones that don't involve weighing them!

I tend to do 2-3 fist sized potatoes per person and 3 extra. Depends on whether the mash is the main veg, with a stew or something, or just one of a few veggies with a meal.

Thank you. I shoudl have just done all of them but thought I had done enough and the rest are enough for the kids tomorrow as boiled. I am doing a roast dinner so there is plenty to eat, just a bit less mash than DD and I woud have liked.