Weight & Body Composition
Every weight & body composition calculator on CalcEngines — each with its formula, a worked example, the standard it follows and the assumptions it makes.
8 calculators in this section
- BMI Calculator (Standard and Asian-Indian Cut-offs)Body mass index from height and weight, in metric or imperial, printed to one decimal place and categorised on that printed figure rather than on the raw float — so the number you can see is the number that chose the row. The standard boundaries are taken from the CDC, a US Government work. The Asian-Indian cut-offs of 23 and 25 from Indian national guidance are shown alongside them and never swapped in silently, because for most readers of this site they are the more relevant pair and because moving somebody's category without telling them is not an improvement. What BMI cannot see is on the page, not in a footnote: it is a ratio of weight to height squared, it was devised as a population statistic, and it knows nothing about muscle, bone, where fat sits, age or ancestry.
- BMR and TDEE Calculator (Mifflin-St Jeor)Basal metabolic rate from the Mifflin-St Jeor equation, then total daily energy expenditure at every rung of the activity ladder at once — because the multiplier is the part of this arithmetic with no published derivation behind it, and the gap between the bottom rung and the top is about 1,100 kcal/day for an average adult. The equation’s own published accuracy is shown as a range beside the figure.
- Body Fat Percentage Calculator (Navy, Skinfold)Two field methods for estimating the proportion of the body that is fat — the US Navy circumference equations in the centimetre form their authors published, and the Durnin and Womersley four-site skinfold equations — computed side by side so that the gap between them is visible. The published errors are on the page rather than behind it, because they are the point: the Navy equations carry a standard error of estimate of 3.52 percentage points in men and 3.72 in women against underwater weighing, and against DXA in independent samples they have been reported biased by anything from 2.3 to 6.0 points. A single confident figure is the misleading output. There is no category, no range and no target here: no reference distribution that could be reproduced on a commercial site was found, and the page says so instead of inventing one.
- Calorie Deficit Calculator: What the Linear Rule Gets WrongWhat daily intake a given amount of weight change over a given number of weeks implies — and, beside it, what the published dynamic model says that intake will actually achieve, which at six months is usually about half. The page refuses rather than answering when the figure would fall below your own estimated basal metabolic rate, or when the rate exceeds 1 kg a week, because a number clamped to a floor looks like an answer.
- Daily Water Intake Calculator (And Where 8×8 Came From)A drinks-per-day figure built from a published adequate intake, minus the water that comes from food, plus what exercise and heat actually cost — and an honest account of why the arithmetic is weak: two expert bodies disagree by 1.2 litres a day on the same question, sweat rates vary tenfold between people, and the famous eight glasses a day has no identifiable evidence behind it. Thirst and urine colour are better guides than this page.
- Macronutrient Split Calculator (Grams From Percentages)Grams of protein, carbohydrate and fat from a total energy figure and a split you choose, at 4, 4 and 9 kcal per gram — with each percentage reported against the published acceptable macronutrient distribution ranges, and against the narrower protein range Australia and New Zealand set from the same evidence. No split is presented as the right one, because the published work does not name one.
- Waist-to-Height Ratio Calculator (the 0.5 Boundary)Waist divided by height, computed from the figures as typed because the ratio is dimensionless, printed to two decimal places and banded on that printed figure so the number you can see is the number that chose the band. The boundary values of 0.4, 0.5 and 0.6 are taken from a CC BY paper that permits reuse here, and the 0.5 boundary is independently recommended by Indian national guidance in its 2025 revision. The reason this page matters more than the waist-to-hip page for this site's readers is the single most relevant fact in the whole category: the BMI values in different ethnic groups equivalent to a BMI of 30 in white adults span 21.5 to 26, and a single waist-to-height boundary of 0.5 has been found acceptable across every ethnic group examined. The band labels here are positions on a scale, not statements about a body, and nothing on the page is a target.
- Waist-to-Hip Ratio Calculator (No Borrowed Thresholds)Waist divided by hip, computed from the figures as typed so no unit conversion enters the ratio, with the arithmetic of the measurement error printed beside it — because where the tape goes matters more here than anything else on the page, and published comparisons of waist sites in the same people differ by up to 6.9 cm in men and 10.1 cm in women. There is no risk threshold on this page and that is deliberate. The sex-specific cut-offs in universal circulation come from a WHO expert consultation, WHO publications are licensed NonCommercial, and this site carries advertising; no other authoritative body publishes a waist-to-hip cut-off, and the one US national guideline that addresses the question recommends against using the ratio at all and gives none. What the page prints instead is the published evidence on what the ratio predicts, and the two waist thresholds that are cleanly licensed.