Fitness Calculator Suite
A single suite for the core body metrics: Body Mass Index (BMI), Basal Metabolic Rate (BMR), Total Daily Energy Expenditure (TDEE), ideal-weight estimates, body-fat percentage, lean body mass and a daily-calorie target. Pick a calculation, enter your details in metric or imperial, and get the result with the method and assumptions shown. Every figure here is a population estimate drawn from established equations — useful for context and planning, but not a measurement of your body and not medical advice.
How to use this tool
- Choose which metric to calculate.
- Select metric or imperial units.
- Enter your weight, height, age and sex; add activity level, goal or body-fat where the chosen calculation needs them.
- Read the result, the method used, and the assumptions.
- Treat every figure as an informational estimate, not a medical assessment.
The formula
Body metrics come from population formulas. BMI relates weight to height; BMR estimates resting energy use; TDEE scales BMR by activity; ideal weight and body-fat use accepted estimation equations. All are estimates, not measurements or diagnoses.
BMI = weight_kg ÷ height_m²
BMR (Mifflin) = 10·kg + 6.25·cm − 5·age + s (s = +5 male, −161 female)
TDEE = BMR × activity_factor
LBM = weight × (1 − bodyfat%)- BMR
- Basal metabolic rate, kcal/day at rest
- TDEE
- Total daily energy expenditure
- activity_factor
- 1.2 (sedentary) … 1.9 (extra active)
These equations describe population averages. Individual metabolism varies, so treat the numbers as informational starting points, not precise targets or medical advice.
Worked examples
BMI
- Given
- 70 kg, 175 cm
- Result
- 22.9 kg/m² (healthy)
BMI = 70 ÷ 1.75² = 22.9, in the healthy-weight band.
BMR
- Given
- 70 kg, 175 cm, 30, male
- Result
- ≈ 1649 kcal/day
Mifflin–St Jeor: 10×70 + 6.25×175 − 5×30 + 5 = 1648.75 kcal/day at rest.
TDEE
- Given
- BMR 1649, moderately active
- Result
- ≈ 2556 kcal/day
TDEE = 1649 × 1.55 ≈ 2556 kcal/day including typical activity.
Frequently asked questions
BMR is the energy your body uses at complete rest just to stay alive. TDEE is your total daily burn including activity — it multiplies BMR by an activity factor from about 1.2 (sedentary) to 1.9 (very active). TDEE is the figure to compare your calorie intake against.
BMI is a quick population screening tool relating weight to height, but it cannot tell muscle from fat or show where fat is stored. A muscular athlete can register as "overweight" while carrying little fat. Use it as one rough indicator among several, not a verdict on individual health.
They are approximations. The BMI-based (Deurenberg) and Navy circumference methods estimate body fat from proxies like height, age and measurements, and can be off by several points versus a direct method such as DEXA. Use them to track trends over time rather than as an exact figure.
The default is Mifflin–St Jeor, currently considered the most accurate general equation, and the tool also shows the Harris–Benedict value for comparison. If you have a reliable body-fat percentage, the Katch–McArdle equation (based on lean mass) can be more accurate for lean, athletic individuals.
It gives an informed starting estimate for calorie needs, but it is not medical or dietary advice. Real energy needs vary with metabolism, health and many other factors, and restrictive dieting should be done under professional guidance. Use the numbers as a starting point and adjust based on your actual results.
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Related reading
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The exact factor, fast mental shortcuts, and the conversions you actually need.
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