Body composition calculators that tell you the whole story
43 free calculators for BMI, body fat, waist ratios, calories and macros. Every one shows your number against the recognised classification systems side by side (WHO standard, WHO Asia-Pacific, and the post-2025 multi-measure framework) and tells you plainly why the answers differ. Honest accuracy bands, safety rails on every calorie target, metric, imperial and stone as equals.
No account, and your measurements are never stored against you: results are computed in your browser, or re-rendered from the link you hold if JavaScript is off.
I want to lose weight: open the full path
All 43 calculators
Body composition
How much of you is fat, muscle and bone, and how that compares with recognised reference ranges. BMI is the quickest screen; the tape-based and index tools here add what BMI cannot see.
BMI Calculator
Free BMI calculator with WHO standard and Asia-Pacific classifications side by side, plus the 2025 multi-measure check. Metric, imperial and stone.
Relative Fat Mass (RFM) Calculator
Estimate body fat percentage from just height and waist with the Relative Fat Mass equation, a 2018 index that beat BMI against DEXA in NHANES data.
Weight loss percentage calculator
Work out what percentage of your starting weight has changed, where that sits against the 5 and 10 per cent clinical marks, and your average weekly rate.
Skinfold Body Fat Calculator (Jackson–Pollock)
Estimate body fat from caliper skinfolds with the Jackson-Pollock 3-site and 7-site equations, showing both the Siri and Brozek density conversions.
Asian BMI Calculator
BMI calculator using the WHO Asia-Pacific classification (23 overweight, 25 obese) shown alongside the standard scale, with the 2004 action points explained.
Body Fat Calculator (US Navy Method)
Estimate body fat from tape measurements with the US Navy circumference method, cross-checked against three independent equations and an honest error range.
Army Body Fat Calculator
Estimate body fat with the military tape method, compare it with the AR 600-9 age-band limits, and see what the Army's 2026 waist-to-height rule changed.
Ideal Body Weight Calculator
The four clinical ideal weight formulas side by side (Hamwi, Devine, Robinson and Miller), each with the BMI it implies at your height, and why they disagree.
Healthy Weight Range Calculator
The WHO healthy weight range for your height in kg, lb or stone, plus where your current weight sits in it, the Asia-Pacific band and the evidence after 65.
Lean Body Mass Calculator
Work out lean body mass from a measured body fat percentage, or compare the Boer, Hume and James predictions with the honest spread between them stated.
FFMI Calculator
Calculate your fat-free mass index, normalised for height, with interpretation bands and the honest error propagation from your body fat estimate.
Body Frame Size Calculator
Estimate a small, medium or large skeletal frame from your height-to-wrist ratio and from elbow breadth, with both published threshold tables shown in full.
Body Recomposition Calculator
Two weigh-ins plus body-fat percent: see fat mass and lean mass change when the scale is almost flat. Same method both times, weeks apart, not mixed.
Fat distribution
Where fat sits matters more than how much you weigh. Waist-based ratios and shape indices capture visceral fat (the kind that drives cardiometabolic risk) with a tape measure and thirty seconds.
Waist Circumference Calculator
Check your waist against the WHO action levels of 94 and 102 cm for men and 80 and 88 cm for women, plus the IDF population lines and waist-to-height ratio.
Body Roundness Index (BRI) Calculator
Work out your Body Roundness Index from height and waist, read it against the NHANES mortality quintiles, and see it beside ABSI, conicity and BAI.
Waist-to-Height Ratio Calculator
Check your waist-to-height ratio against the evidence-backed bands. Keep your waist under half your height, a better risk screen than BMI alone.
Waist-to-Hip Ratio Calculator
Calculate your waist-to-hip ratio against the WHO risk thresholds of 0.90 for men and 0.85 for women, with the waist circumference cut-offs alongside.
Visceral Fat Calculator
A tape proxy for central fat: waist-to-height 0.5, WHO 94/102 and 80/88 cm lines, and body roundness index. Not a VAT volume scan. Use the WHO waist point.
Calories & nutrition
What your body burns, what to eat to maintain, lose or gain at a safe pace, and how to split it into protein, carbohydrate and fat. Every target here carries its error band and is capped by safety rails written into the code.
Calorie Surplus Calculator
Plan a lean-gain calorie surplus with the rails built in: the weekly rate capped at 0.5% of bodyweight, the surplus at 20% of maintenance, protein included.
TDEE Calculator
Calculate total daily energy expenditure from Mifflin–St Jeor BMR and your activity level, with the honest ±10–15% error band no one else shows you.
BMR Calculator
Work out basal metabolic rate with Mifflin–St Jeor, Harris–Benedict, Katch–McArdle, Cunningham and Owen side by side, with the spread between them stated.
Calorie Deficit Calculator
Plan a weight-loss calorie target with built-in safety rails: capped at 1% of bodyweight weekly, never below 80% of TDEE or the 1,200/1,500 kcal floors.
Macro Calculator
Turn your calories into daily protein, carbohydrate and fat targets in grams: protein set per kilogram of bodyweight, fat floored for hormones.
Protein Intake Calculator
Daily protein in grams from the RDA floor of 0.8 up to 2.2 g per kilogram, with an older-adult tier, per-meal splits and a target from lean mass.
Water Intake Calculator
Your daily fluid estimate in litres, US cups or UK pints, set beside the EFSA and Institute of Medicine reference intakes, with honest, sourced caveats.
Weight Loss Time Calculator
See weeks to a goal at 0.25, 0.5, 0.75 and 1% of bodyweight a week, after the same calorie floors as the deficit tool. No crash-diet date is printed.
Weight Loss Check-In Calculator
Compare expected kilograms from (TDEE minus intake) times days over 7,700 with the scale, then hold, relog, take a diet break, or slow down.
Reverse Diet Calculator
Raise daily calories 50, 100 or 150 kcal a week from your current intake up to estimated TDEE, with a week-by-week table. Early scale drift is often water.
Calories in Body Fat Calculator
See days and weeks to lose a set amount of fat at 7,700 kcal per kg, the same constant as 3,500 kcal per lb. The last kilogram is slower than the first.
Metabolic Age Calculator
See the age whose BMI-22 Mifflin BMR matches yours. It is a gym-scale marketing label, not a tissue age or a medical test. Lean mass is what moves BMR.
Intermittent Fasting Calculator
Plan 14:10, 16:8, 18:6 or 5:2 around estimated TDEE. Weekly calories still rule. Fasting is meal timing, not extra fat burn. Protein must still fit.
Alcohol Calorie Calculator
See typical drink calories against estimated TDEE and a moderate walk. Weekly sittings add up faster than a Tuesday scale shows. Mixers are extra energy.
Fibre Intake Calculator
See daily fibre targets side by side: EFSA 25 g, IOM adequate intake 38/25 g, and 14 g per 1,000 kcal on your energy intake. Raise grams slowly with water.
Fitness & training
Numbers for the gym and the road: heart-rate training zones, strength estimates and the energy cost of activities, each from a named formula with its limits spelled out.
Calories burned calculator
Calories burned by activity from published MET values, showing the net figure trackers leave out, MET-minutes, and how the session reads against WHO guidance.
One-rep max (1RM) calculator
Estimate your one-rep max from a set taken close to failure. Seven published equations, the spread between them, and the load for every training percentage.
Heart rate zone calculator
Work out your five heart rate training zones from age and resting pulse, with Tanaka, Gellish and 220 minus age compared and the error band stated.
VO₂ max calculator
Estimate VO2 max from a heart rate ratio, a 12-minute run, a one-mile walk or a 1.5-mile test, each with the error band its own paper published.
Walking Calorie Calculator
Estimate walking calories from 2011 Compendium METs, kilometres, steps and the share of a WHO 150-minute, 500 MET-minute week. Treat a MET as plus or minus 20%.
Running Calorie Calculator
Estimate running calories from Compendium METs by pace: gross and net kcal, kilometres and kcal per km. Same sources as the walking tool. Plus or minus 20%.
Clinical measures
Measures you may meet on a hospital worksheet or a child's growth chart, explained plainly and computed exactly as the published references define them, never as a substitute for the clinician using them.
Child and Teen BMI Percentile Calculator
Work out a child or teenager's BMI percentile on the CDC growth reference, for ages 2 to 20. Adult BMI categories do not apply to a growing body.
Child Growth Percentile Calculator
Height and weight percentiles and z-scores on the CDC growth charts for ages 2 to 20, plus a mid-parental target adult height with its honest error band.
Pregnancy weight gain calculator
The 2009 Institute of Medicine weight gain ranges for pregnancy, set by pre-pregnancy BMI, with the weekly rate and the range expected at the week you are now.
Body Surface Area Calculator
Body surface area from height and weight in all six published formulas (Mosteller, Du Bois, Haycock, Gehan, Fujimoto, Takahira) with the clinical context.
How BodyStats is different
Every classification, side by side
WHO standard, WHO Asia-Pacific and the 2004 action points are three distinct, citable systems. We show them together and label each, instead of collapsing them into one muddled table.
Honest error bands, printed with the result
A tape body fat estimate is ±3–4 points against DEXA; a TDEE figure carries ±10–15%. Those bands appear next to the numbers, not in a footnote.
Safety limits enforced in code
Calorie targets are capped at 1% of bodyweight a week and 80% of TDEE, with hard floors of 1,500 kcal for men and 1,200 for women. There is no aggressive mode to switch on.
No medical review claimed
No page here carries a reviewer byline, because no clinician has been contracted to review it. Instead every threshold traces to primary literature you can check yourself.
One bibliography for the whole site
Every study, standard and government publication cited anywhere on BodyStats is listed once, grouped by topic, with the link resolved. Where a constant has no primary source, the page that uses it says so.
It works with JavaScript off
Calculators post to the server and come back rendered, so a locked-down device still gets the result. Content pages ship no JavaScript at all and load in a fraction of a second on a slow connection.
Measure first: the number is only as good as the tape
Half a centimetre of tape position moves every waist-based result more than a fortnight of dieting does. The first three steps, in full:
- Time it right. Measure first thing in the morning, after using the bathroom and before eating or drinking. Waist circumference swings 2–3 cm through an ordinary day with food and fluid.
- Find the landmark. Stand and find the midpoint between your lowest rib and the top of your hip bone (iliac crest). For most people this is at or just above the navel. Measuring at the navel itself is the common convention and fine, as long as you use the same landmark every time.
- Position the tape. Wrap the tape level all the way around. Check in a mirror that it isn't riding up at the back. Directly on skin, not over clothing.
Start with the reasoning
26 sourced explainers cover where each formula came from and where it stops being trustworthy. Browse all guides.
What changed in the 2025 obesity definition
The Lancet Commission's 2025 framework ended BMI-alone diagnosis: BMI now needs a fat-distribution measure, plus a clinical/preclinical split.
How to measure your waist accurately
The exact landmark, tape technique and timing for a waist measurement you can trust, the half-centimetre details that move every waist-based result.
BMI vs body fat vs waist ratio: which number matters?
Three measurements, three different questions. What each can and cannot tell you, where they disagree, and the two-measure combination to use.
Questions people ask first
Which calculator should I start with?
Start with the BMI calculator and add a waist measurement. That pair covers the two questions that matter most for screening (is total mass high for your height, and is fat stored centrally), and current clinical guidance asks for both rather than BMI alone. If your BMI is raised but your waist is not, the body fat and FFMI calculators will describe a muscular build far better. If you are planning intake rather than screening, start with TDEE instead.
Why do two calculators give me different classifications for the same body?
Because recognised classification systems are calibrated on different populations for different purposes. The WHO standard BMI cut-offs came largely from European cohorts; the WHO Asia-Pacific categories sit lower because many Asian populations carry more body fat and face higher cardiometabolic risk at the same BMI. Most sites quietly pick one table and never say which. Every page here shows the systems side by side, labelled, so you can see exactly where you stand under each.
How accurate are these calculators?
Each result prints its own honest error band: the tape-based body fat method runs about three to four percentage points either side of a DEXA scan, and any TDEE estimate carries roughly ten to fifteen percent uncertainty because activity multipliers are population averages. Formula-only measures like BMI, waist ratios and body surface area are exact arithmetic on your inputs; their uncertainty lives in what they can and cannot see, which each page explains.
Is anything I enter stored or sent anywhere?
No measurement is stored against you. There is no account, no profile and no way to join a calculation back to a person. Results are computed in your browser, or re-rendered from the link you hold when JavaScript is off. Your unit preference stays in your own browser's storage. The privacy page sets out the anonymous, unlinkable counts we keep to know which calculators are used.
Are these calculators medical advice?
No. Every tool here implements a published population-level formula with known limits, and says where those limits are. They cannot account for your medications, conditions, pregnancy or athletic background. Where a judgement genuinely needs a clinician (telling preclinical from clinical obesity, or any calorie target below the safety floors), the site stops and says so rather than guessing.
How often should I re-measure?
Weekly for weight, monthly for tape measurements, and not at all for the rest unless something has changed. A tape reading moves by a centimetre for reasons that have nothing to do with fat (hydration, a large meal, the time of day, where the tape sat), so measuring daily records noise and reads it as progress or failure. A month is long enough for real change to clear that noise. Weight is noisy too, which is why the weight-change tools here work on a rolling average rather than a single morning.
Which body fat method should I trust at home?
None of them individually, and that is the honest answer. A tape estimate runs about three to four percentage points either side of a DEXA scan, skinfold calipers depend heavily on the person pinching, and bathroom impedance scales swing with hydration. What all three do well is track direction: measured the same way at the same time of day, a series tells you whether you are gaining or losing fat even when the absolute figure is wrong. Pick one method, keep it, and read the trend rather than the number.
Can I use these calculators for a child?
Only the ones written for children. Adult BMI categories, body fat ranges and calorie formulas do not apply under 18, because a growing body's composition changes with age and sex in ways a fixed cut-off cannot capture. Use the child BMI calculator, which reads a percentile from the CDC reference for the child's exact age and sex, and treat anything it says as a conversation to have with a GP or child health nurse rather than a reason to change how a child eats.
Do these work without JavaScript?
Yes. Every calculator posts its measurements to the server and the page comes back rendered with your result, so the tools work with scripting disabled, on a locked-down work device, or on a connection that dropped the script. With JavaScript on, the same calculation runs in your browser and updates as you type. The content pages themselves ship no JavaScript at all, which is why they load quickly on a slow phone connection.