Mashed potatoes go with almost anything, from Christmas turkey to fried chicken, pot roast or a rack of barbecue ribs. It can be challenging to judge how many potatoes you need to prepare to feed your family or guests. In general, each pound of raw potatoes makes about 420 g (2 cups) of mashed potatoes. The exact number of potatoes you need depends on how much you want to serve each person and what size potatoes you use.
Write out the menu for the meal you are serving and count the number of side dishes in your menu. If potatoes are your only accompaniment, make a large portion for each person. If you have one or two other veg, make a medium portion for each person. If you have three or more other accompaniments, as is the case with Christmas dinner, make a small portion for each person.
Multiply the number of people you are serving by the number of ounces of potato you want in each portion. A large portion should have 227 g (8 oz) of potato, a medium should have 170 g (6 oz) and a small should have 113 g (4 oz). For example, if you are serving 12 people a medium-sized portion, you need 2 kg (70 oz) of potato.
You might have to convert your kilograms to pounds in order to follow some recipes. There are roughly 2.18 pounds to a kilogram.
Divide the number of kilos of potatoes by the average weight of each potato to find out how many you need. Most medium-sized potatoes weigh about 151 g, (1/3 lb) whereas smaller potatoes only weigh 113 g (1/4 lb) or less and very large potatoes could weigh more than 500 g. For example, if you are buying medium-sized potatoes, you will need approximately 13 potatoes.
Use a kitchen scale or supermarket scale to weigh the potatoes for a more accurate measurement. If you are unsure of the amount you want, and do not mind having leftover mashed potatoes, add one or two people to the number you use in Step 2.