Per-serving numbers:
calories and cost from one pot of food

One pot, two questions: what does a plate contain and cost?

Calories per serving and cost per serving come from the same list of ingredients and the same final division. You total the whole pot, decide how many equal portions it makes, and divide. The totals can be wildly different from a guess made by eye, because oil, ghee and sugar carry far more calories per gram than most cooks assume.

People ask for the first number to manage intake and the second to keep a household budget or price a tiffin or catering order. Doing both in one pass is efficient: one table, two extra columns.

The step that goes wrong most often is not the maths but the definition of a serving. A recipe that says it serves 4 but is eaten as 3 larger plates has a different answer on both counts. Decide the portion first, ideally in grams of cooked food or in a fixed katori, then divide.

The two formulas

Both use raw, as-purchased weights. Water absorbed during cooking adds grams but not calories, so rice weighed after cooking looks lower in kcal per 100 g than rice weighed dry. Weigh dry and divide by servings, or weigh the finished pot and portion by weight.

If you work from fat, protein and carbohydrate grams instead, the usual conversion factors are about 4 kcal per gram of protein, 4 per gram of carbohydrate and 9 per gram of fat. Labels round, so a sum of the three will not always match the printed kcal exactly.

Worked example: a six-serving rajma and rice pot

The prices and calorie values below are typical, not authoritative. Substitute your own prices and the kcal figures from your packs.

Notice what dominates. Rice and rajma give 79% of the energy, while oil gives 15% from a small spoonful. That is why changing the oil quantity moves the answer more than swapping the tomatoes ever could.

Portion size drives everything. The same pot cut into 5 plates is 2,378.5 ÷ 5 = 476 kcal and ₹20.60 a plate, while 6 plates gave 396 kcal and ₹17.17. Neither number is wrong; they describe different plates, which is why you should write the portion size next to the figure when you share it.

Small recipe edits are easy to test the same way. Cutting the oil from 40 g to 20 g removes 20 × 9 = 180 kcal from the pot, so each of the six plates falls from 396 to about 366 kcal, a cut of roughly 30 kcal. A few lines in a notebook or a calculator are enough to see whether a change is worth making.

Reading a pack label: per 100 g versus per serving

Packs print two columns. The per-100 g column is for comparing products fairly. The per-serving column depends on the manufacturer's chosen portion, which can be surprisingly small.

To get your own portion, scale the per-100 g value. A snack that lists 150 kcal per 100 g gives 150 × 40 ÷ 100 = 60 kcal for a 40 g handful. A pack of 200 g contains 300 kcal in total, however many servings the packet claims.

Nutrient reference values on labels are typically based on a 2,000 kcal day, so a 400 kcal plate is about a fifth of that. Individual needs vary a great deal with age, size and activity, and a dietitian is the right person to set a personal target.

Costs the ingredient list hides

• Trim and waste. If onions lose about 10% in peeling, usable onion costs ₹30 ÷ 0.90 = ₹33.33 per kg, not ₹30.
• Fuel, water and a share of spices bought once and used for months. Give them a flat per-batch amount, like the ₹15 above.
• Cooking loss in meat and vegetables, which changes the number of servings if you portion by weight.
• Price changes. Vegetable prices swing weekly, so a cost-per-plate figure is a snapshot, not a constant.

For a food business the next figure is food cost percentage: cost per serving divided by selling price. At ₹17.17 cost and a ₹60 price that is 28.6%. Many outlets aim for roughly 28–35%, but the right target depends on rent, labour and the menu, so use it as a loose guide.

Mistakes that make the numbers lie

Most errors are structural, not arithmetic. Because the final answer is a single tidy number, a wrong input hides easily, and nobody checks a result that looks reasonable.

• Dividing by the number of people at the table, not by equal portions measured out.
• Mixing raw weights with cooked weights in the same table.
• Leaving out cooking oil, butter or sugar added at the end because it was a casual pour.
• Counting calories for a full pack when only a share was used.
• Using the price of the big pack for a one-time purchase of a small packet.

Batch cooking and weighing out portions

Cooking for a week at once is where per-serving numbers earn their keep. Make the whole batch, weigh the finished pot, subtract the weight of the empty vessel and divide by the number of containers. Each box then holds the same share of the calories and the cost.

Suppose the cooked pot weighs 2,400 g net and you want eight boxes. Each box is 300 g, and its share is 1/8 of the pot's totals. If you later eat a single 450 g plate from the same pot, it contains 450 ÷ 2,400 = 18.75% of the calories and of the cost, which is more than a standard box. Weighing the plate is more reliable than counting spoons.

Recording the per-100 g value of the cooked dish also helps with leftovers. Total calories divided by cooked weight in grams, times 100, gives a figure you can reuse for any portion of that batch, and it becomes the label you would otherwise be missing.