FFMI

Tool id: ffmi · Methods: standard

Compute the Fat-Free Mass Index (FFMI) and its height-adjusted form from weight and body fat percentage (or lean mass directly), and flag whether the result exceeds the ~25 natural ceiling (Kouri et al. 1995).

Input

Field	Type	Notes
height	{ value, unit }	cm or in — required
weight	{ value, unit }	kg or lb — required
body_fat	number | null	body-fat %, 2–70; required if lean_mass is absent
lean_mass	{ value, unit } | null	fat-free mass — alternative to body_fat; if both are given, lean_mass wins
methods	string[] | "all"	defaults to "all"

Methods

• standard — FFMI = fat-free mass (kg) ÷ height (m)². The adjusted value normalizes to a 1.8 m reference: FFMI + 6.1 × (1.8 − height_m) (Kouri et al. 1995). above_natural_limit is true when the adjusted FFMI exceeds 25 (the ceiling is defined on the height-normalized value).

The ~25 ceiling comes from a male reference population; the practical natural limit for women is lower (~22). The flag uses the single 25 threshold — read it with that in mind.

Example

TypeScript

import { REGISTRY } from "@almostjacked/fitness-tools";
const ffmi = REGISTRY.get("ffmi")!;
ffmi.compute(ffmi.input.parse({
  height: { value: 170, unit: "cm" },
  weight: { value: 80, unit: "kg" },
  body_fat: 12,
}));

curl

curl -s localhost:8080/v1/tools/ffmi \
  -X POST -H 'content-type: application/json' \
  -d '{"height":{"value":170,"unit":"cm"},"weight":{"value":80,"unit":"kg"},"body_fat":12}'

MCP

Call the ffmi tool with these arguments:

{
  "height": { "value": 170, "unit": "cm" },
  "weight": { "value": 80, "unit": "kg" },
  "body_fat": 12
}

{
  results: [
    {
      method: "standard",
      value: 24.36,
      unit: "kg/m²",
      detail: {
        ffm_kg: 70.4,
        ffmi_adjusted: 24.97,
        above_natural_limit: false,
      },
    },
  ],
  consensus: null,
}

Call it another way

Full docs for the other protocols: HTTP API · MCP server.