Free Online Health & Body Measurement Calculators
Twelve free health calculators for BMI, BMR, TDEE, body fat, lean mass, ideal weight and heart rate zones, each using a published clinical formula.
Calculate Body Mass Index in metric or imperial units, see your WHO category, healthy weight range and where you sit on the BMI scale. Free tool.
Calculate your basal metabolic rate with the Mifflin-St Jeor, Harris-Benedict or Katch-McArdle formula and see your maintenance calories by activity.
Calculate ideal body weight with the Devine, Robinson, Miller and Hamwi formulas, compare the results and see the healthy BMI range for your height.
Estimate body fat percentage with the US Navy circumference method or the BMI-based Deurenberg formula, and see your fat mass and lean mass split.
Calculate your waist-to-hip ratio and see your WHO risk category, how to measure correctly and why WHR predicts risk that BMI on its own misses.
Calculate waist-to-height ratio, the keep-your-waist-under-half-your-height screening measure, with your risk band and how to measure properly.
Calculate your total daily energy expenditure from BMR and activity level, then see calorie targets and macro splits for loss, maintenance or gain.
Estimate calories burned over a distance walking, running or cycling, using MET values adjusted for your weight, pace and terrain. Free calculator.
Calculate lean body mass with the Boer, James and Hume formulas, compare the three results and see your fat mass and lean mass percentage split.
Determine small, medium or large body frame from wrist circumference or elbow breadth, and see how frame size adjusts your ideal weight target.
Calculate your five training heart rate zones with the Karvonen reserve method or max-HR percentages, including warm-up, fat burn and VO2 max.
Calculate Body Adiposity Index from hip circumference and height to estimate body fat percentage without a scale, and compare BAI against BMI.
Every calculator here names its formula
Body measurement calculators are only as good as the equation behind them, and most sites do not tell you which one they used. Every calculator in this category states its formula, cites the researcher who published it, and shows the working. That matters because different published formulas give genuinely different answers for the same person — the Devine and Hamwi ideal-weight equations can disagree by several kilograms, and neither is wrong.
| Calculator | Formula used | What it estimates |
|---|---|---|
| BMI | Quetelet index, WHO categories | Weight relative to height |
| BMR | Mifflin-St Jeor, Harris-Benedict, Katch-McArdle | Calories burned at complete rest |
| Daily calories (TDEE) | BMR × activity factor | Total daily energy expenditure |
| Body fat | US Navy circumference method; Deurenberg | Percentage of mass that is fat |
| Lean body mass | Boer, James, Hume | Mass excluding fat |
| Ideal body weight | Devine, Robinson, Miller, Hamwi | Reference weight for a height |
| Waist-to-hip ratio | WHO risk thresholds | Fat distribution |
| Waist-to-height ratio | Ashwell boundary values | Central adiposity |
| Body adiposity index | Bergman BAI equation | Body fat without a scale |
| Body frame size | Wrist circumference / elbow breadth | Skeletal frame category |
| Heart rate zones | Karvonen reserve method; %HRmax | Five training intensity bands |
| Calories by distance | Compendium MET values | Energy cost of a walk, run or ride |
Start with BMI, then stop relying on it
BMI is a screening measure, not a diagnosis. It was designed by Adolphe Quetelet in the 1830s to describe populations, and it does that job well. Applied to one person it has a specific, well documented weakness: it cannot tell muscle from fat, and it says nothing about where fat sits. A muscular athlete and a sedentary person of the same height and weight get the same BMI and are in quite different health situations.
This is why the category includes four other measures of the same underlying question. Waist-to-height ratio is the single most useful follow-up: it needs one tape measurement, it captures central fat — the kind associated with metabolic risk — and its rule of thumb is memorable, namely keep your waist under half your height. Body fat percentage and lean body mass then split your weight into the two components BMI collapses into one.
How the energy calculators fit together
They are a chain, and running them out of order produces nonsense. BMR is what your body burns doing nothing at all — keeping you breathing, warm and circulating. Multiply it by an activity factor and you get TDEE, the calories you actually spend in a normal day. A deficit or surplus is then applied to TDEE, never to BMR: eating at your BMR is a severe restriction, not a moderate one.
Mifflin-St Jeor is the default because it has held up best against measured data in the general population. Katch-McArdle is more accurate if you know your body fat percentage, because it works from lean mass rather than total weight, which is why it suits lean and athletic bodies better. Harris-Benedict is the oldest of the three and tends to run high.
Why calorie figures are estimates and always will be
Predictive equations were fitted to population samples. Individual metabolic rate varies by roughly ±10% around the prediction for reasons including thyroid function, genetics and non-exercise activity thermogenesis. Treat any number these tools produce as a starting point to adjust from after two or three weeks of real-world feedback, not as a fixed target.
Measuring properly matters more than picking the right formula
The circumference-based tools are sensitive to technique, and a badly taken measurement will swamp any difference between equations.
- Waist: at the midpoint between the lowest rib and the top of the hip bone, not at the navel and not at the belt line. Measure at the end of a normal exhale, tape snug but not compressing the skin.
- Hip: at the widest point of the buttocks, tape level all the way round.
- Neck (for the US Navy method): just below the larynx, tape sloping slightly downward at the front.
- Measure at the same time of day, ideally in the morning before eating, and take the average of two readings.
An honest note on what these tools are for
These calculators are educational. They implement published formulas correctly and show you the working, which is more than many sites do, but they are screening and tracking aids — not a medical assessment. No equation can see your blood pressure, your lipid panel, your family history or your medication. If a result concerns you, or if you are pregnant, under 18, an older adult, or managing a chronic condition, the right next step is a conversation with a clinician rather than a different calculator.