A "Better Homes and Gardens" cookbook recipe for mashed potatoes calls for 0.454kg. of potatoes for every four servings. Ochef.com recommends using between a third to a half a pound of potatoes per person in mashed potato recipes. To serve a crowd of 40 people, the majority of recipes require approximately 6.8kg. of potatoes.
Recipes and Potatoes May Vary
A quick Internet search reveals hundreds, if not thousands of variations of recipes for mashed potatoes, causing number of potatoes needed to vary. Also, no one has established a set standard for measuring a small, medium, large or extra large potato.
To determine how many potatoes to purchase, check the specific recipe you are using and divide the pounds of potato called for by the number of servings. Once you know how much potato is required for a single serving, you can multiply that number by the number of guests to determine the amount of potatoes needed
Weighing the potatoes with the scales provided in the supermarket's produce department will ensure you're purchasing the correct amount of potatoes for the recipe.