# Boer estimated lean body mass

Boer LBM

Status: LIVE
Price: $0.005 USDC
`GET /api/calc/ffm`
HTML: https://magentlab.com/docs/ffm
Markdown: https://magentlab.com/docs/ffm.md

Not a medical device. Not a diagnosis, dose, or listing recommendation.

## What it computes

Compute Boer 1984 sex-specific estimated lean body mass from height, weight, and sex.

## When to use

When an agent already has sex, height, and weight and must not invent kilograms, apply James or Hume formulas, or treat the result as a dosing weight or measured body composition.

## When not to use

- Not a medical device. Not a dosing weight. Boer 1984 estimated lean body mass to normalize body fluid volumes; magent does not measure body composition.
- Boer 1984 sex-specific estimated lean body mass only. Does not apply James or Hume formulas.
- Height 100-220 cm and weight 20-300 kg are magent clamps, not published Boer input bands.
- Does not report fat mass. magent does not measure the patient.

## Formula

```
male: LBM_kg = 0.407 × weight_kg + 0.267 × height_cm − 19.2; female: LBM_kg = 0.252 × weight_kg + 0.473 × height_cm − 48.3
```

## Citation

[Estimated lean body mass as an index for normalization of body fluid volumes in humans](https://doi.org/10.1152/ajprenal.1984.247.4.F632)
Boer P
Am J Physiol. 1984;247(4 Pt 2):F632-F636
DOI: [10.1152/ajprenal.1984.247.4.F632](https://doi.org/10.1152/ajprenal.1984.247.4.F632)

## Worked example

### Female 60 kg, 163 cm

Given: `height_cm=163, sex=female, weight_kg=60`

1. female: LBM_kg = 0.252 × 60 + 0.473 × 163 − 48.3
2. 15.12 + 77.099 − 48.3 = 43.919 → 43.9


## Also searched as

- estimated lean body mass
- Boer LBM
- Boer 1984 lean body mass
- fat-free mass Boer
- lean body mass height weight
- estimated LBM
- Boer FFM

## Parameters

- `sex` (string, required): Sex used by Boer 1984 (separate male and female estimated lean-body-mass equations).
- `weight_kg` (number, required): Weight in kilograms (20-300, magent clamp; Boer 1984 does not publish an input band).
- `height_cm` (number, required): Height in centimeters (100-220, magent clamp; Boer 1984 does not publish an input band).

## Bulk (POST)

POST the same path with a JSON items array. The first item is the GET unit; each additional item is $0.002. Invalid items return HTTP 400 before settlement.

Method: `POST /api/calc/ffm`
Max items: 25
Price: unit_amount + extra_item_amount * (n - 1) (unit 5000 atomic, extra 2000 atomic)
Status: PREVIEW

- 1 to 25 items. Each item uses the same keys as the GET query parameters.
- POST of 1 item costs the same as GET. Lists longer than 25: chunk into multiple POSTs. Extra items still execute; do not pad dummy rows.
- The first invalid item fails the whole request (index in the 400 JSON). You are not charged.
- HTTP 200 is {count, path, items}. Each items[i] is the GET 200 body for that row.
- Catalog misses (empty matches, found=false) stay paid 200s inside that slot.
- x402 resource URL is this path plus n and body_sha256. Browsers that prefer text/html get the same paywall as GET; Pay retries POST with the same items.

Example request:

```json
{
  "items": [
    {
      "height_cm": "163",
      "sex": "female",
      "weight_kg": "60"
    },
    {
      "height_cm": "163",
      "sex": "female",
      "weight_kg": "60"
    }
  ]
}
```

Human paywall (two-item fixture): https://api.magentlab.com/paywall/bulk/ffm

Example 200:

```json
{
  "count": 2,
  "path": "/api/calc/ffm",
  "items": [
    {
      "disclaimer": "Not a medical device. Deterministic published-formula or published-code output for autonomous agents. A licensed clinician remains responsible for patient care and billing submissions.",
      "citation": {
        "authors": "Boer P",
        "doi": "10.1152/ajprenal.1984.247.4.F632",
        "id": "boer-1984",
        "pmid": "6496691",
        "source": "Am J Physiol. 1984;247(4 Pt 2):F632-F636",
        "title": "Estimated lean body mass as an index for normalization of body fluid volumes in humans"
      },
      "formula": "boer_lbm",
      "formula_expression": "male: LBM_kg = 0.407 × weight_kg + 0.267 × height_cm − 19.2; female: LBM_kg = 0.252 × weight_kg + 0.473 × height_cm − 48.3",
      "sex": "female",
      "weight_kg": 60.0,
      "height_cm": 163.0,
      "ffm_kg": 43.9,
      "lbm_kg": 43.9
    },
    {
      "disclaimer": "Not a medical device. Deterministic published-formula or published-code output for autonomous agents. A licensed clinician remains responsible for patient care and billing submissions.",
      "citation": {
        "authors": "Boer P",
        "doi": "10.1152/ajprenal.1984.247.4.F632",
        "id": "boer-1984",
        "pmid": "6496691",
        "source": "Am J Physiol. 1984;247(4 Pt 2):F632-F636",
        "title": "Estimated lean body mass as an index for normalization of body fluid volumes in humans"
      },
      "formula": "boer_lbm",
      "formula_expression": "male: LBM_kg = 0.407 × weight_kg + 0.267 × height_cm − 19.2; female: LBM_kg = 0.252 × weight_kg + 0.473 × height_cm − 48.3",
      "sex": "female",
      "weight_kg": 60.0,
      "height_cm": 163.0,
      "ffm_kg": 43.9,
      "lbm_kg": 43.9
    }
  ]
}
```

## Response fields

- `formula` (string): boer_lbm
- `formula_expression` (string): Exact Boer 1984 expressions used
- `sex` (string): female or male
- `weight_kg` (number): Weight in kg used
- `height_cm` (number): Height in cm used
- `lbm_kg` (number): Boer 1984 estimated lean body mass in kg, 1 decimal (paper term)
- `ffm_kg` (number): Alias of lbm_kg; same Boer 1984 estimate, not a measured fat-free mass
- `citation` (object): Boer 1984 citation
- `disclaimer` (string): Not-a-device notice

## Example JSON

Frozen fixture. Not a live lookup.

```json
{
  "disclaimer": "Not a medical device. Deterministic published-formula or published-code output for autonomous agents. A licensed clinician remains responsible for patient care and billing submissions.",
  "citation": {
    "authors": "Boer P",
    "doi": "10.1152/ajprenal.1984.247.4.F632",
    "id": "boer-1984",
    "pmid": "6496691",
    "source": "Am J Physiol. 1984;247(4 Pt 2):F632-F636",
    "title": "Estimated lean body mass as an index for normalization of body fluid volumes in humans"
  },
  "formula": "boer_lbm",
  "formula_expression": "male: LBM_kg = 0.407 × weight_kg + 0.267 × height_cm − 19.2; female: LBM_kg = 0.252 × weight_kg + 0.473 × height_cm − 48.3",
  "sex": "female",
  "weight_kg": 60.0,
  "height_cm": 163.0,
  "ffm_kg": 43.9,
  "lbm_kg": 43.9
}
```

## Errors

- HTTP 400 `invalid_ffm`: Fat-free mass needs sex, weight_kg, and height_cm as used in Boer 1984. Returned before settlement; you are not charged.
- HTTP 400 `invalid_items`: POST body must be a JSON object with only an items array Returned before settlement; you are not charged.
- HTTP 400 `invalid_item_count`: items must be an array of 1 to 25 objects Returned before settlement; you are not charged.
- HTTP 400 `invalid_item`: each items entry must be a JSON object Returned before settlement; you are not charged.

Shared HTTP 402 and 503: https://magentlab.com/docs/payments

## Related tools

- [Devine IBW](https://magentlab.com/docs/ibw) — Compute Devine ideal body weight and 0.4 adjusted body weight from height, sex, and actual weight.
- [BMI](https://magentlab.com/docs/bmi) — Compute Keys/Quetelet body-mass index from height and weight, plus a WHO adult band.

## Payment

Unpaid requests return HTTP 402 even if query parameters or POST items are missing or invalid, so CDP and agents can index the path. After a PAYMENT-SIGNATURE, invalid params return HTTP 400 JSON before settlement. magent does not charge. Fix the params, then request a new 402 quote for that complete URL. Catalog misses (empty matches, found=false) are valid paid 200s.

- GET the tool with Accept: application/json (do not send Accept: text/html unless you want the human paywall).
- HTTP 402 means you have not paid. Decode the base64 PAYMENT-REQUIRED header. HTTP 503 is not a new quote.
- Sign accepts[0] (exact, EIP-3009) with validBefore = now + maxTimeoutSeconds (600 seconds), or accepts[1] (batch-settlement deposit/voucher) on product GET. Ping and POST {items} stay exact. Magent retries transient facilitator 429/5xx before answering.
- Retry the same URL with PAYMENT-SIGNATURE (base64 JSON of accepted and payload). Magent attaches canonical extensions.bazaar on CDP verify/settle; echoing 402 bazaar is optional.
- Success is HTTP 200 JSON plus PAYMENT-RESPONSE. exact settles before the tool. batch-settlement verifies (and deposit-settles) before the tool and commits the charge after HTTP 2xx. HTTP 503: retry the same PAYMENT-SIGNATURE. Mint a new exact nonce only after a new HTTP 402.

- offered `exact` on eip155:8453: Fixed-price USDC on Base. The buyer authorizes the advertised amount (EIP-3009). magent settles before the tool runs (paymentFlow upfront). extra.assetTransferMethod=eip3009 extra.paymentFlow=upfront.
- offered `batch-settlement` on eip155:8453: Payment-channel vouchers claimed later in batches. Exact stays accepts[0]. Same-path POST {items} is still exact. extra.assetTransferMethod=eip3009 extra.paymentFlow=authorization.

- not offered `upto`: Not offered. Usage-based: buyer authorizes a ceiling, seller settles the actual amount after work. Reserved for a future metered tool. Not for current calculators or code search.

Same-path POST {items} is still scheme exact: one EIP-3009 authorization for GET unit plus $0.002 per extra item. That is not x402 batch-settlement (payment channels / vouchers).

Shared HTTP 402 and 503 table: https://magentlab.com/docs/payments

Stdio MCP (one process per host): https://magentlab.com/docs/mcp

## Guarantees

- HTTP 402 is unpaid, including a missing query. After PAYMENT-SIGNATURE, invalid parameters return HTTP 400 before settlement. You are not charged. HTTP 402 never includes the tool JSON.
- exact: settlement finishes before the tool (paymentFlow upfront). batch-settlement: verify/deposit before the tool; chargedCumulativeAmount commits after HTTP 2xx. Uncertain or failed settlement fails closed (HTTP 503). Retry the same PAYMENT-SIGNATURE.
- HTTP 402 is unpaid only. Do not sign a second authorization because of a 503.
- Execution is timeout-bounded and concurrency-capped.
- Calculator inputs are stored encrypted for allowlisted operators (Magent Console). They are not in public logs, SSH lookups, catalog, or rollups. Request logs store path without query.