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Katch-McArdle BMR Calculator
Estimates basal metabolic rate with the Katch-McArdle formula (BMR = 370 + 21.6 × lean body mass in kg), which uses body-fat percentage instead of height, sex and age, and multiplies it by a standard activity factor for total daily energy expenditure.
When to use
You know body-fat percentage (especially for lean or very muscular people, whom weight-based equations misestimate) and want resting and daily calorie needs.
Do not use when: Body-fat percentage is unknown or guessed (use bmr / tdee with Mifflin-St Jeor instead), or for children, pregnancy or clinical nutrition; informational, not medical advice.
Formula
lean_body_mass_kg = weight_kg × (1 − body_fat_percent / 100); bmr_kcal = 370 + 21.6 × lean_body_mass_kg; bmr_kj = bmr_kcal × 4.184; tdee_kcal = bmr_kcal × activity multiplier (sedentary 1.2, light 1.375, moderate 1.55, active 1.725, very_active 1.9)
The Katch-McArdle equation (McArdle, Katch & Katch, Exercise Physiology; closely related to Cunningham's 1980 equation 500 + 22 × LBM) predicts resting energy from fat-free mass alone, so it is independent of sex and age; its accuracy is bounded by the accuracy of the body-fat estimate. Informational, not medical advice.
Inputs
| Parameter | Type | Unit | Required | Description |
|---|---|---|---|---|
weight_kg | number | kg | yes | Body weight in kilograms. Range: > 0, ≤ 400 |
body_fat_percent | number | % | yes | Body-fat percentage (calipers, DEXA, BIA or a tape-measure estimate). Range: ≥ 2, ≤ 70 |
activity_level | enum: sedentary | light | moderate | active | very_active | default sedentary | Weekly exercise level; maps to the standard multipliers 1.2 / 1.375 / 1.55 / 1.725 / 1.9. |
Outputs
| Output | Type | Unit | Description |
|---|---|---|---|
lean_body_mass_kg | number | kg | weight_kg × (1 − body_fat_percent / 100). |
fat_mass_kg | number | kg | weight_kg × body_fat_percent / 100. |
bmr_kcal | number | kcal/day | 370 + 21.6 × lean body mass. |
bmr_kj | number | kJ/day | bmr_kcal × 4.184. |
activity_multiplier | number | Factor applied to BMR for the chosen activity level. | |
tdee_kcal | number | kcal/day | bmr_kcal × activity_multiplier: estimated maintenance calories. |
Example
80 kg, 15 % body fat, moderate activity: {"weight_kg":80,"body_fat_percent":15,"activity_level":"moderate"} → {"lean_body_mass_kg":68,"bmr_kcal":1838.8,"bmr_kj":7694,"activity_multiplier":1.55,"tdee_kcal":2850.1}
65 kg, 28 % body fat, sedentary: {"weight_kg":65,"body_fat_percent":28} → {"lean_body_mass_kg":46.8,"bmr_kcal":1380.9,"tdee_kcal":1657.1}
GET https://tttkmbb.com/api/v1/calculate/katch-mcardle-bmr?weight_kg=80&body_fat_percent=15&activity_level=moderate
Machine access
- API:
GET https://tttkmbb.com/api/v1/calculate/katch-mcardle-bmr(query parameters) orPOSTwith a JSON body{"inputs": {...}} - Schema: https://tttkmbb.com/api/v1/calculators/katch-mcardle-bmr · Markdown: https://tttkmbb.com/fitness/katch-mcardle-bmr.md · JSON definition: https://tttkmbb.com/fitness/katch-mcardle-bmr.json
- MCP: server
https://tttkmbb.com/mcp, toolrun_calculator with calculator_id="katch-mcardle-bmr" - OpenAPI operationId:
calculate_katch_mcardle_bmr - Freshness:
static. Authentication: none. Rate limit: fair use (see rate limits).
Sources
FAQ
When is Katch-McArdle better than Mifflin-St Jeor?
When body-fat percentage is measured reasonably well and the person is unusually lean or muscular; for typical adults with only weight and height, Mifflin-St Jeor is at least as accurate.
Why is there no sex or age input?
Sex and age mostly affect resting metabolism through their effect on lean mass, which this formula takes directly.
Related calculators
- BMR Calculator — Mifflin-St Jeor and Harris-Benedict estimates without body fat.
- TDEE Calculator — Calorie targets for loss or gain from a weight-based BMR.
- Skinfold Body Fat Calculator — Caliper body-fat percentage for this formula.