BMI calculator
Body mass index is weight over height squared. It is a crude screen rather than a measure of fitness, and it cannot tell muscle from fat, so read it alongside a body-fat estimate.
BMI Calculator
Body mass index is weight in kilograms divided by height in metres squared. A BMI below 18.5 is underweight, 18.5 to 24.9 is normal, 25 to 29.9 is overweight, and 30 or above is obese. BMI cannot distinguish muscle from fat, so trained people frequently read as overweight despite low body fat.
Overweight
Method notes (1)
- BMI doesn't distinguish fat from lean mass — high-muscle individuals can read overweight without excess fat. Pair with body_fat_pct (estimate_body_fat) for a fuller picture.
Metric or imperial · runs the same code as the app · nothing is sent anywhere
How it works
BMI = weight in kg / (height in m)². The healthy band shown is the weight range that puts you between a BMI of 18.5 and 24.9 at your height.
Categories follow the WHO adult cutoffs: under 18.5 underweight, 18.5 to 24.9 normal, 25 to 29.9 overweight, and 30 or above obese, which splits further into classes one, two and three at 35 and 40.
Common questions
Why does BMI say I am overweight when I lift?
Because it only knows your weight and height. Muscle is denser than fat, so trained people routinely land in the overweight band with low body fat. Use the FFMI or body-fat calculator instead, which account for composition.
Is BMI useless then?
Not useless, just narrow. It works reasonably well across large populations and as a first screen. It fails on individuals at the extremes of muscularity, and it says nothing about where fat sits on the body.
The other calculators
Body composition
What you are made of, and what you could be.
- Ideal weight calculatorFour classic formulas that predict a target weight from height and sex alone.Ideal weight
- Body fat calculatorThree ways to estimate body fat without a DEXA scan.Body fat
- FFMI / Lean body mass calculatorYour lean body mass (muscle, bone, organs and water), your fat mass, and the fat-free mass index, which scales lean mass to height so that unlike BMI it tracks how much muscle you carry.FFMI / Lean body mass
- Maximum muscular potential calculatorWrist and ankle circumference are proxies for skeletal frame size, and frame size predicts how much muscle you can ultimately carry.Max potential
- Ideal body proportions calculatorClassical proportions scale every girth from the wrist, because wrist size tracks your skeletal frame and barely changes with training or fat.Ideal proportions
- Body shape calculatorClassifies your body shape from a few tape measurements: hourglass, spoon, triangle, rectangle and the rest for women, V-taper to oval for men.Body shape
Energy
What you burn, and what to eat against it.
- TDEE, BMR & macro calculatorYour total daily energy expenditure is what you burn across a whole day, training included.TDEE, BMR & macros
- Calorie deficit calculatorPick a goal weight and a pace.Calorie deficit
- Water intake calculatorA daily drinking target from your bodyweight, with extra for training and hot weather.Water intake
Strength
What you lift, and how it ranks.
- One-rep max calculatorEstimate a maximum from a set you have actually done, without the risk of testing a true single.One-rep max
- RPE calculatorRate of perceived exertion turns how hard a set felt into numbers.RPE
- Strength level calculatorRank any lift against population strength standards for your bodyweight and sex, with an optional age adjustment.Strength level
- Powerlifting score calculatorRaw totals favour heavier lifters, so powerlifting uses coefficients to compare across bodyweight.Wilks & DOTS
- Strength symmetry calculatorComparing raw numbers across different lifts tells you nothing, because a 200 kg deadlift and a 100 kg bench are not equivalent achievements.Symmetry
- Barbell plate calculatorTells you what to hang on each side of the bar for a target weight, and whether the number is reachable at all with standard plates.Plate loading
- Warm-up sets calculatorA ramp from the empty bar to your top set: the weight gets heavier while the reps get fewer, so you arrive warm but not tired.Warm-up sets
- Training volume calculatorEnter up to three exercises with sets, reps and load.Training volume
Cardio & burn
Aerobic fitness and the cost of a session.
- VO₂max & heart rate zone calculatorTwo answers from the same three numbers.VO₂max & HR zones
- Steps to calories calculatorTurns a step count into distance and calories using your stride and bodyweight, and shows how it compares with the daily step range linked to better health at your age.Steps → calories
- Workout calorie calculatorEstimates the energy cost of an activity from its metabolic equivalent, your bodyweight and how long you did it.Activity burn
- Lifting calorie calculatorMost calculators give weight training a flat per-hour figure.Lifting burn
These numbers are more useful when something tracks them.
The app runs this same maths against your logged weigh-ins, meals and sessions, so the figure updates itself instead of being a one-off.
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