How the Potato Calculator Works
This calculator estimates how many potatoes — and how much total weight — you need to buy for a meal. It starts from a standard per-person serving size that depends on how the potatoes will be prepared, scales that by the number of people you're feeding, adds a buffer for peeling and trimming waste, and finally converts the total weight into a whole number of potatoes using the average weight of a single potato.
Formula and method
The calculation runs in three steps:
- Raw serving weight = Number of people × serving size per person (in grams), where the serving size depends on the dish style: about 150 g for a mashed or boiled side dish, 175 g for roasted potatoes or fries, 250 g when potatoes are the main starch, and 200 g (roughly one medium potato) for a whole baked potato.
- Total weight to buy = Raw serving weight × (1 + waste buffer ÷ 100), where the waste buffer accounts for skins, eyes, and trim lost during peeling.
- Potatoes needed = ⌈Total weight to buy ÷ average weight per potato⌉, rounded up to the next whole potato since you cannot buy a fraction of one.
Choosing the right serving size
Serving size is the biggest lever in the result, so pick the dish style that matches what you're actually cooking. A side dish of mashed or roasted potatoes needs less per person than a plate where potatoes are the main component, and a whole baked potato is sized to the potato itself rather than a scoop size — which is why it uses close to one full potato per person.
Common sources of error
- Using cooked weight instead of raw weight: potatoes lose water and mass when boiled or roasted, so recipe serving sizes given in cooked weight will overstate how much raw potato you need if entered directly.
- Skipping the waste buffer: peeling and trimming typically remove 10-15% of a potato's weight; leaving the buffer at 0% will leave you short at the register.
- Guessing the average potato weight: potato sizes vary widely by variety and grade — a bag labeled "medium" can range from about 140 g to 220 g, which shifts the potato count noticeably.
Applications
This kind of per-person scaling is useful for grocery shopping before a dinner or holiday meal, scaling a recipe up or down for a different guest count, and rough catering or potluck planning where you need a purchase quantity rather than a precise recipe measurement. Always round up when buying, since it is easier to have a spare potato than to run short mid-recipe.