# US Navy Body Fat Percentage Calculator

> US Navy Body Fat Percentage Calculator is a paid API for AI agents from fitness-calc.x402tookit.com, paid per call via x402, $0.02/call, status unknown (last checked 2026-10-29).

Estimates body fat percentage using the US Navy tape-measure method, returning fat mass, lean mass, and body composition category from circumference measurements.

## Facts

- Endpoint: GET https://fitness-calc.x402tookit.com/body-fat-navy?utm_source=zero.xyz
- Price: $0.02/call
- Payment: x402
- Status: unknown
- Last checked: 2026-10-29
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/us-navy-body-fat-percentage-calculator-f900b166
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_qI6uw7yJR8xMxf3pDLEzg

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 us-navy-body-fat-percentage-calculator-f900b166
```

Example prompt: I'm a 5'11" male weighing 185 lbs — can you estimate my body fat percentage using the Navy method? My neck is 16 inches, my waist is 34 inches, and use imperial units.

## When to prefer this

Use this endpoint when you need a non-invasive, tape-measure-based body fat estimate following the standardized US Navy method. It is ideal when DEXA or caliper data is unavailable and the user can provide neck, waist, and (for women) hip circumference measurements. Prefer this over BMI for body composition analysis since it differentiates fat from lean mass. Also suited for military or occupational fitness assessments that specifically reference the Navy formula.

## Known failure modes

- Missing required parameters (sex, height, neck, waist) returns an error
- Hip measurement missing for female input causes failure
- Out-of-range measurements (e.g. negative or implausibly large values) may return degraded result with reasons
- Invalid unit string (not 'metric' or 'imperial') may default to metric or return an error
- Weight not provided means fat mass and lean mass cannot be computed (only percentage returned)

## How this service works

Body fat percentage estimate from tape measurements (US Navy method) with fat mass, lean mass and a general category.

## Output

Returns the estimated body fat percentage (bodyFatPct), fat mass in kg (fatMassKg), lean mass in kg (leanMassKg), a body composition category (e.g. 'fitness', 'obese'), the sex used, input measurements converted to inches, a summary verdict, and a medical disclaimer. Includes a degraded flag and reasons array if any inputs were outside expected ranges.

## 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"
     ],
     "type": "string"
    },
    "queryParams": {
     "type": "object",
     "required": [
      "sex",
      "height",
      "neck",
      "waist"
     ],
     "properties": {
      "hip": {
       "type": "number",
       "description": "Hip at the widest point (required for women)"
      },
      "sex": {
       "type": "string",
       "description": "male or female"
      },
      "neck": {
       "type": "number",
       "description": "Neck circumference below the larynx"
      },
      "units": {
       "type": "string",
       "description": "metric (cm, kg; default) or imperial (inches, lb)"
      },
      "waist": {
       "type": "number",
       "description": "Waist at the navel (men) or narrowest point (women)"
      },
      "height": {
       "type": "number",
       "description": "Height"
      },
      "weight": {
       "type": "number",
       "description": "Body weight to also give fat and lean mass"
      }
     }
    }
   },
   "additionalProperties": false
  },
  "output": {
   "type": "object",
   "required": [
    "type"
   ],
   "properties": {
    "type": {
     "type": "string"
    },
    "example": {
     "type": "object",
     "properties": {
      "sex": {
       "type": [
        "null",
        "string"
       ]
      },
      "asOf": {
       "type": [
        "null",
        "string"
       ]
      },
      "source": {
       "type": [
        "null",
        "string"
       ]
      },
      "reasons": {
       "type": [
        "array",
        "null"
       ],
       "items": {
        "type": "string"
       }
      },
      "summary": {
       "type": [
        "null",
        "string"
       ]
      },
      "verdict": {
       "type": [
        "null",
        "string"
       ]
      },
      "category": {
       "type": [
        "null",
        "string"
       ]
      },
      "degraded": {
       "type": [
        "boolean",
        "null"
       ]
      },
      "fatMassKg": {},
      "bodyFatPct": {
       "type": [
        "null",
        "number"
       ]
      },
      "disclaimer": {
       "type": [
        "null",
        "string"
       ]
      },
      "leanMas
… (truncated)
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/us-navy-body-fat-percentage-calculator-f900b166/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from fitness-calc.x402tookit.com](https://www.zero.xyz/host/fitness-calc.x402tookit.com/llms.txt)