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Food & Nutrition Guides
Part of the CalcProMaster guides library · Calories, macros & kitchen math
Nutrition advice collapses without arithmetic: how many calories your body actually needs, how protein maps to body weight, and how a recipe scales from four plates to forty without the seasoning going wrong.
Methodology: Published nutrition data and standard macro and calorie methods, using accepted energy conversions.
Nutrition maths lives or dies on the portion: whether a label figure is per 100 g or per serving, whether the ingredient is weighed raw or cooked, and whether the batch actually scales linearly.
How the math works
Nutrition math starts with TDEE: BMR × activity multiplier. For the calculators’ example adult — 70 kg, 30 years, 175 cm — Mifflin-St Jeor lands near 1,650 kcal BMR; a moderate multiplier of 1.55 brings TDEE to roughly 2,550 kcal. A 500 kcal daily deficit then predicts about half a kilogram of loss per week — slowly and noisily, not linearly.
Protein targets are simpler than supplement marketing suggests: 0.8 g/kg is the RDA floor for sedentary adults; 1.2–2.0 g/kg fits active training or ageing bodies. For an 80 kg lifter at 1.6 g/kg, that’s 128 g/day — spreadable across three meals; precision beyond that earns nothing.
Calorie Guide
BMR, activity multipliers and honest deficit math.
Unit Conversion Guide
Cups, grams and millilitres — kitchen conversions that go wrong.
BMI Guide
What BMI does and doesn’t say about a body.
How do I calculate my daily calorie needs?
BMR via Mifflin-St Jeor (10 × kg weight + 6.25 × cm height − 5 × age + sex offset), then × an activity factor from 1.2 (sedentary) to 1.9 (very active). That maintenance figure is what you adjust up or down.
How much protein do I need per day?
The RDA floor is 0.8 g per kg of body weight; 1.2–2.0 g/kg supports active training or older adults. The protein need calculator applies your weight and goal directly.
Related guides
What this category covers
These calculators handle portion maths, recipe scaling, nutrition per serving and food-cost comparisons. The formulas are simple; the difficulty is in units, serving sizes and whether a label describes the food as sold or as eaten.
Because the inputs are small numbers, a mistake of one unit silently doubles the answer. Reading the label carefully is a larger part of the work than the arithmetic.
Raw, cooked and drained
Rice roughly triples in weight when cooked, pasta doubles, and meat loses about a quarter of its weight to moisture. A nutrition table built on raw weight cannot be applied to a cooked portion without adjusting for that water.
Canned goods add another state: drained weight is not the same as the label weight. For anything sold in brine or syrup, use the drained figure the label provides.
Serving size versus portion size
A label serving is an administrative unit chosen by the manufacturer, and it is frequently smaller than what people eat. Two servings in a bottle is common and easy to miss.
Multiply by the number of servings you actually ate, not by the number in the package. That single step fixes most of the discrepancy between tracked intake and observed results.
Where these answers go wrong
- Comparing a per-100 g label value with a per-serving recipe figure without converting the weight first.
- Using raw weights for foods that lose water when cooked — cooked meat is roughly a quarter lighter than the same piece raw.
- Scaling salt and leavening straight with the batch when only the quantity changed, not the pan or the rise time.
- Reading calorie estimates as exact when labels are permitted to differ from the stated value.
Frequently asked questions
Why do my macros add up to more calories than the label?
Because the label rounds. Protein and carbohydrate are about 4 kcal per gram and fat about 9, so multiplying the rounded gram figures and adding them can land a few percent away from the stated total. Neither number is wrong; they are rounded at different stages.
How much does cooking change a weight?
It depends on the method and the food. Grilled or roasted meat loses roughly a quarter of its weight as water and fat, while grains and pasta gain weight by absorbing water. That is why a nutrition plan has to say whether it counts raw or cooked, and use the same one throughout.
Are carb limits from keto calculators exact?
No. The threshold at which a person stays in ketosis varies with activity, insulin sensitivity and how the carbs are timed. The calculators give a commonly used starting range, and the honest way to use it is as a starting point to adjust against how you actually respond.
Worked example: Daily Calorie Needs at its default inputs
This is the answer Daily Calorie Needs gives before you touch anything — the defaults as shipped, computed live rather than copied from a sample.
| Input | Default |
|---|---|
| Age | 30 |
| Weight (kg) | 70 |
| Height (cm) | 170 |
Result: 2507 cal/day
Age — three values, three answers
Same calculator, same fields, one change: age.
| Age | Result |
|---|---|
| 15 | 2623 cal/day |
| 30 | 2507 cal/day |
| 45 | 2391 cal/day |
If the rows barely differ, age is not your lever — change a different input. If they swing widely, get that number right before trusting the total.
Try the matching calculators
Daily Calorie Needs Macro Split Calculator Recipe Scaler
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