Body & Weight Calculators

Measuring a body honestly

"What should I weigh?" sounds like one question, but it hides at least four: how does my weight compare with the population, how much of me is fat rather than muscle and bone, where is that fat sitting, and what would a sensible target look like for my frame? No single number answers all four, which is why this shelf holds eight calculators rather than one. Each tool uses a published formula, names it, and shows the working, so you can see not just your number but where it came from and what it deliberately ignores.

The tools split into three groups: the population-scale measures built on BMI, the composition measures that estimate fat and lean mass directly, and the target-setters that turn height and frame into a weight range worth aiming for.

The BMI family: quick, standard, and honest about its limits

The BMI Calculator is the natural starting point. Body mass index is your weight in kilograms divided by your height in metres squared, and the standard adult categories are fixed: under 18.5 is underweight, 18.5 to 24.9 is the healthy range, 25 to 29.9 is overweight, and 30 or above is obesity. The calculator turns those boundaries back into real weights for your height; at 1.75 m the healthy window runs from 56.7 kg to 76.3 kg, a spread of nearly twenty kilograms, and that width is the point. It also flags what BMI misses: the index cannot tell muscle from fat, so trained people routinely read 25 to 28 while carrying modest body fat.

Two neighbouring tools build on the same scale. The Healthy Weight Calculator presents the full healthy range for your height, marked against your own weight and waist, with the BMI cut-offs behind it shown in both kilograms and pounds; it answers "what should I weigh for my height?" as a range rather than a single flattering number. The Overweight Calculator tackles the blunter question, "am I overweight?", and deliberately refuses to answer from BMI alone. It reads your BMI category and your waist-circumference risk band together, tie-breaking with waist-to-height ratio (the target is under 0.5), and returns one combined verdict. When BMI and waist disagree, the waist usually deserves more weight, because it tracks where fat sits rather than how much of you there is.

Body composition: fat, lean mass and frame

Estimating body fat with a tape measure

The Body Fat Calculator uses the circumference method the US Navy has relied on since the 1980s: neck, waist and height for men, with hips added for women, feed a formula that estimates body fat percentage without callipers or scales that guess. Alongside the percentage you get the category it lands in and your lean-mass and fat-mass split in actual kilograms, which is often the more useful pair of numbers; two people at 80 kg with 15 and 30 per cent body fat are in very different situations that a bathroom scale cannot distinguish.

The Army Body Fat Calculator implements a different tape test: the one-site abdomen-and-weight formula from AR 600-9 that the US Army adopted in June 2023, replacing its older multi-site method. The calculator checks your result against the Army's age-and-sex standard and compares it with the Navy method, which is worth doing, because the two formulas can disagree on the same body. If you are preparing for a real tape test, this is the tool that mirrors the regulation; for general fitness tracking, the Navy method is the more common choice.

Lean mass and body type

The Lean Body Mass Calculator estimates everything that is not fat, comparing the Boer, James and Hume formulas side by side, and switching to the direct method when you already know your body fat percentage. Lean body mass matters more than most people expect: it drives your energy needs, it is what protein targets are usually scaled to, and preserving it is the difference between weight loss and fat loss.

The Body Type Calculator handles the softest question on this shelf with unusual honesty. It reads your frame size from a wrist-to-height ratio and returns a disclosed blend across the classic ectomorph, mesomorph and endomorph descriptions rather than stamping you with a single fixed label, because real bodies are mixtures and the somatotype system was never as scientific as gym folklore suggests.

Setting a target: what should the goal weight be?

The Ideal Weight Calculator compares four classic formulas, Devine, Robinson, Miller and Hamwi, side by side with the healthy BMI range for your height. These formulas were originally built for clinical purposes such as drug dosing, and they disagree with each other by several kilograms, which the calculator shows rather than hides. Read the spread as a zone, not a bullseye. Between the four formulas and the BMI window from the Healthy Weight Calculator, a sensible personal target is usually obvious; a single "ideal" figure to the decimal point never was.

Using several tools together

A thorough self-check takes about ten minutes and three tools. Start with the BMI Calculator for the population-scale category, add the Body Fat Calculator to see how much of your weight is actually fat, and run the Overweight Calculator to fold your waist measurement into a combined verdict. If the results point towards losing or gaining, the Lean Body Mass Calculator tells you what to protect on the way, and the diet-side tools on the Calories & Nutrition shelf, particularly the Calorie Deficit Calculator, turn the target into a daily plan. Everything here is free and prints its formula on the page, so a surprising result can always be traced back to its inputs.

Mistakes these pages see most often

• Treating one BMI point as meaningful. A reading of 25.4 carries almost the same risk as 24.9; the direction of travel over a year matters far more than a boundary crossing.
• Measuring the waist in the wrong place or over clothing. Circumference methods live or die on consistent tape placement; each calculator explains exactly where to measure.
• Chasing a single ideal weight. Four respected formulas disagree by several kilograms; the healthy range is the honest answer.
• Weighing daily and reacting to noise. Water, food timing and hormones swing daily weight by a kilogram or more; weekly averages tell the real story.

Frequently asked questions

Is BMI useless if I lift weights?

Not useless, but less informative. Muscle is denser than fat, so trained people often read overweight on the BMI Calculator while lean. Pair it with a waist-to-height check; if your ratio is under 0.5 and you train hard, the BMI category is probably flattering the scale rather than warning you. A body fat estimate settles it.

How accurate is the Navy tape method?

Good enough to track yourself with, provided you measure the same way each time. It estimates from circumferences, so it can drift a few percentage points from a lab measurement, but its trend over months is reliable, which is what most decisions actually need.

Why do the ideal weight formulas disagree?

Devine, Robinson, Miller and Hamwi were derived at different times from different populations, mostly for clinical dosing rather than aesthetics. The Ideal Weight Calculator shows all four precisely so you can treat the spread as a range instead of trusting any one of them too literally.

Which single measurement matters most?

If forced to pick one, waist-to-height ratio: keep your waist under half your height. It is the tiebreaker the Overweight Calculator uses because it tracks the abdominal fat most linked to health risk, and it needs nothing but a tape measure.