What this calculator does
Mashed potato is planned from the finished serving backwards. Eight guests at 200 g each need 1,600 g of mash, and allowing 20% for peeling and moisture loss means buying 2,000 g of raw potatoes.
The loss allowance is the part people forget, and it runs higher than expected. Peeling alone takes 10 to 15% depending on how the potatoes are shaped and how careful you are, and there is further loss to trimming and to water driven off in cooking. Twenty percent is a reasonable overall figure and erring higher costs very little.
The formula
The finished mash needed is the guest count multiplied by the serving size. The raw potato weight divides that by one minus the loss percentage, which scales up to account for what is removed before and during cooking. The cup figure uses roughly 240 g of mash per cup.
| Term | Meaning |
|---|---|
| Serving size | Finished mash per person. Around 200 g is a generous side serving; 150 g is modest. |
| Peel and moisture loss | Weight removed by peeling and driven off in cooking, typically 15 to 25% combined. |
| Raw weight | What to buy, which is the figure the loss allowance produces. |
The inputs explained
| Field | What to enter |
|---|---|
| Guests | Number of guests. |
| Serving size per person (g) | Finished mash per person in grams. 200 g is a generous side; use 150 g where there are several other sides. |
| Peel & moisture loss (%) | Combined peeling and cooking loss as a percentage. 20% is a reasonable default. |
When to use it
Shopping for a large meal
Converting a guest count into a bag weight is the whole task, and the loss allowance is what stops it coming up short.
Scaling a family recipe
Recipes written for four scale linearly, and the raw weight calculation handles the conversion from the finished quantity the recipe describes.
Planning for leftovers
Mash reheats acceptably and makes other dishes, so many cooks deliberately over-cater. Raising the serving size rather than the loss percentage is the honest way to do that.
Worked examples
Every figure in the tables below is produced by this page’s own calculator at build time, so the numbers and the tool always agree. Select any row to load that scenario.
How many potatoes does each guest count need?
A range of guest counts at a generous serving size.
| Guests | Raw potatoes to buy | In pounds | Finished mash | Finished mash in cups (≈240 g/cup) |
|---|---|---|---|---|
| 4 | 1,000 g | 2.20 lb | 800 g | 3.3 |
| 8 | 2,000 g | 4.41 lb | 1,600 g | 6.7 |
| 12 | 3,000 g | 6.61 lb | 2,400 g | 10.0 |
| 20 | 5,000 g | 11.02 lb | 4,000 g | 16.7 |
Questions
How many potatoes per person for mash?
About 250 g of raw potatoes per person for a generous 200 g serving, once peeling and cooking loss are allowed for. For a more modest side alongside several others, 150 g of mash from about 190 g raw is sufficient.
Which potatoes are best for mashing?
Floury varieties such as Maris Piper, King Edward or Russet, which break down readily and absorb butter and milk well. Waxy potatoes hold together and produce a denser, gluier mash, particularly if worked hard.
Why does the raw weight exceed the mash by more than the loss percentage?
Because the percentage is of the raw weight, not the finished weight. Losing 20% of the raw leaves 80%, so recovering a given finished weight means dividing by 0.8, which is multiplying by 1.25. A 20% loss therefore needs 25% more raw material.
Can I make mash ahead?
Yes, and it reheats reasonably in a low oven or over a pan of hot water, with a little extra milk stirred through. It is better made a few hours ahead than a day, since it firms up considerably in the fridge and needs vigorous reheating that can make it gluey.
For the rest of a party spread, see the BBQ party planner. For ham to serve alongside, see the ham per person calculator.