How this calculator works
A portion of mashed potato is usually planned by volume or by weight, and the two are close: a US cup of mash weighs about 210 g, so half a cup is a little over 100 g and a generous scoop is around 200 g. The calculator multiplies the portion by the number of people to get the finished mash, then works backwards to the raw ingredients using the shares you set. Potato dominates the mass, milk loosens the mash and butter enriches it, so the raw potato figure is lower than the finished weight: a kilogram of mash does not need a kilogram of raw potatoes once milk and butter are counted. Raw peeled potatoes lose a little water during boiling and gain some back from the milk, so the default shares assume roughly even in and out.
Formula
total mash = people x portion. potatoes = total mash x potato share. milk = total mash x milk share. butter = total mash x butter share. salt = total mash x 0.008, which is about 1 percent of the finished weight. A cup of mash is taken as 210 g.
Worked example
For 8 people at 200 g each the total is 1600 g, or 1.6 kg of mash. At the default shares that is 1600 x 0.80 = 1280 g of raw potatoes, 1600 x 0.14 = 224 g of milk (about 217 mL) and 1600 x 0.06 = 96 g of butter. Salt comes to 1600 x 0.008 = 12.8 g. By volume, 8 people at 0.95 cup each is 7.6 cups of mash, which at 210 g a cup is 1596 g, almost the same plan.
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Frequently asked questions
How much mashed potato is a serving?
About 200 g, or a little under a cup, is a generous side portion for a holiday meal. A smaller 100 to 150 g portion suits a buffet with many other sides. Canada's Food Guide counts 125 mL of a starchy side as one serving, which is about 105 g of mash.
Which potatoes are best for mashing?
Floury, high starch potatoes such as russet or Yukon Gold mash light and smooth. Waxy potatoes hold their shape and turn gluey when mashed. The calculator works by weight, so the variety only changes the texture and the amount of milk the potatoes will take.
Why is the raw potato weight lower than the mash?
The finished dish includes milk and butter, and the potato itself is most of the total but not all of it. If you want a mash that is nearly all potato, raise the potato share and lower the milk and butter shares; the ratio has to stay at or below 100 percent.
Can I make it ahead?
Yes. Mash holds well in a covered dish over a pan of hot water or in a slow cooker on low, with a little extra milk stirred in before serving. Keep it out of the temperature danger zone: hot food should stay above 60 C until it is served.