# Boer 1984 Lean Body Mass (Fat-Free Mass) Calculator

> Boer 1984 Lean Body Mass (Fat-Free Mass) Calculator is a paid API for AI agents from api.magentlab.com, paid per call via x402, $0.005/call, status unknown (last checked 2026-09-14).

Estimates lean body mass (LBM/FFM) in kilograms using the Boer 1984 sex-specific equations from height and weight inputs.

## Facts

- Endpoint: GET https://api.magentlab.com/api/calc/ffm
- Price: $0.005/call
- Payment: x402
- Status: unknown
- Last checked: 2026-09-14
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/boer-1984-lean-body-mass-fat-free-mass-calculator-9f67ca12
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_RRFF6UfVMOmDYEck4uC_g

Status and success rate cover calls made through Zero and Zero's own probes. Third-party monitors may report differently.

## How to call it through Zero

Zero handles the 402 payment challenge and records the run. With the Zero CLI installed (`npm i -g @zeroxyz/cli`):

```sh
zero fetch --capability boer-1984-lean-body-mass-fat-free-mass-calculator-9f67ca12
```

Example prompt: Using the Boer 1984 formula, estimate the lean body mass for a male patient who is 178 cm tall and weighs 85 kg.

## When to prefer this

Choose this endpoint when you specifically need the Boer 1984 estimated lean body mass equation and not the James, Hume, or Peters formulas. It is the right choice for reference weight computations in pharmacokinetics or anesthesia research workflows where Boer is the specified formula. Do not use this for actual body composition measurement, dosing weight (which has different conventions), or when a different LBM formula is required.

## Known failure modes

- Missing required parameter (sex, weight_kg, or height_cm) returns a 4xx error
- Height below 100 cm or above 220 cm triggers magent clamp behavior (clamped, not errored)
- Weight below 20 kg or above 300 kg triggers magent clamp behavior
- Invalid sex value (not 'male' or 'female') returns a validation error
- Payment not provided or insufficient returns HTTP 402

## How this service works

Boer 1984 estimated lean body mass from sex, height_cm, and weight_kg (male 0.407W+0.267H-19.2; female 0.252W+0.473H-48.3). Reports lbm_kg (paper term) with ffm_kg as the same alias. Height 100-220 cm and weight 20-300 kg are magent clamps, not Boer bands. Not a dosing weight, James/Hume formula, or measured body composition. magent does not measure the patient.

## Output

Returns lbm_kg (lean body mass in kilograms), also aliased as ffm_kg (fat-free mass), computed via the Boer 1984 sex-specific linear regression equations. Male: 0.407×weight_kg + 0.267×height_cm − 19.2; Female: 0.252×weight_kg + 0.473×height_cm − 48.3. Inputs are clamped to height 100–220 cm and weight 20–300 kg by the API.

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "$schema": "https://json-schema.org/draft/2020-12/schema",
 "required": [
  "input"
 ],
 "properties": {
  "input": {
   "type": "object",
   "required": [
    "type",
    "method"
   ],
   "properties": {
    "type": {
     "type": "string",
     "const": "http"
    },
    "method": {
     "enum": [
      "GET",
      "HEAD",
      "DELETE"
     ],
     "type": "string"
    },
    "headers": {
     "type": "object",
     "additionalProperties": {
      "type": "string"
     }
    },
    "queryParams": {
     "type": "object",
     "required": [
      "sex",
      "weight_kg",
      "height_cm"
     ],
     "properties": {
      "sex": {
       "enum": [
        "female",
        "male"
       ],
       "type": "string",
       "description": "Sex used by Boer 1984 (separate male and female estimated lean-body-mass equations)."
      },
      "height_cm": {
       "type": "number",
       "description": "Height in centimeters (100-220, magent clamp; Boer 1984 does not publish an input band)."
      },
      "weight_kg": {
       "type": "number",
       "description": "Weight in kilograms (20-300, magent clamp; Boer 1984 does not publish an input band)."
      }
     }
    }
   },
   "additionalProperties": false
  },
  "output": {
   "type": "object",
   "required": [
    "type"
   ],
   "properties": {
    "type": {
     "type": "string"
    },
    "example": {
     "type": "object"
    }
   }
  }
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/boer-1984-lean-body-mass-fat-free-mass-calculator-9f67ca12/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from api.magentlab.com](https://www.zero.xyz/host/api.magentlab.com/llms.txt)