# Saylor Innovations Body Fat Calculator (US Navy Method)

> Saylor Innovations Body Fat Calculator (US Navy Method) is a paid API for AI agents from saylorinnovations.com, paid per call via x402, $0.01/call, status unknown (last checked 2026-10-18).

Calculates body fat percentage from tape measurements using the US Navy formula, returning ACE category, healthy range, and optionally fat and lean mass in kg

## Facts

- Endpoint: GET https://saylorinnovations.com/api/health/body-fat?utm_source=zero.xyz
- Price: $0.01/call
- Payment: x402
- Status: unknown
- Last checked: 2026-10-18
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/saylor-innovations-body-fat-calculator-us-navy-method-5796bc52
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_SnQvSpSlsdHaBNnTEnypX

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 saylor-innovations-body-fat-calculator-us-navy-method-5796bc52
```

Example prompt: Can you calculate my body fat percentage using the US Navy tape-measure method? I'm male, 178 cm tall, neck is 38 cm, waist is 85 cm, and I weigh 80 kg.

## When to prefer this

Choose this endpoint when you need a quick, formula-based body fat estimate from simple tape measurements without requiring expensive lab tests or body scan equipment. It is ideal for fitness, wellness, or health-tracking agents that need to classify body composition using the widely-accepted US Navy method. Prefer it over BMI-based endpoints when you want a more accurate fat-vs-lean breakdown, and over DEXA or bioimpedance APIs when only circumference measurements are available.

## Known failure modes

- Missing required query parameters (sex, height_cm, neck_cm, waist_cm) result in an error response
- Invalid or non-numeric values for measurements may cause calculation failure
- Unrealistic measurement values (e.g. neck larger than waist) may produce nonsensical but technically computed results
- Hip measurement may be required for female calculations — omitting it for female inputs could cause an error
- Network or upstream service downtime returns a non-200 response

## How this service works

Body fat percentage from tape measurements using the US Navy method with ACE category, healthy range and fat and lean mass when weight is supplied

## Output

Returns a JSON object with the computed body fat percentage, the ACE category (e.g. Fitness, Acceptable, Obese), the healthy range as a percentage string, the method and source used, the inputs echoed back, and — if weight was provided — fat mass and lean mass in kilograms, plus an optional note for context.

## 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_cm",
      "neck_cm",
      "waist_cm"
     ],
     "properties": {
      "sex": {
       "type": "string",
       "description": "male or female"
      },
      "neck_cm": {
       "type": "string",
       "description": "Neck circumference in cm"
      },
      "waist_cm": {
       "type": "string",
       "description": "Waist circumference in cm"
      },
      "height_cm": {
       "type": "string",
       "description": "Height in cm"
      },
      "weight_kg": {
       "type": "string",
       "description": "optional, to compute fat and lean mass"
      }
     }
    }
   },
   "additionalProperties": false
  },
  "output": {
   "type": "object",
   "required": [
    "type"
   ],
   "properties": {
    "type": {
     "type": "string",
     "const": "json"
    },
    "example": {
     "type": "object",
     "required": [
      "sex",
      "body_fat_percent",
      "category"
     ],
     "properties": {
      "sex": {
       "type": "string",
       "description": "Sex used in the formula"
      },
      "note": {
       "type": "string",
       "description": "Caveat or context for reading the result"
      },
      "inputs": {
       "type": [
        "object",
        "null"
       ],
       "description": "Measurements used: height, neck, waist and hip in cm"
      },
      "method": {
       "type": "string",
       "description": "Method used"
      },
      "source": {
       "type": "string",
       "description": "Data source the values come from"
      },
      "category": {
       "type": "string",
       "description": "Category"
      },
      "fat_mass_kg": {
       "type": [
        "number",
        "null"
       ],
       "description": "Fat mass, in kilograms"
      },
      "lean_mass_kg": {
       "type": [
        "number",
        "null"
       ],
       "description": "Lean mass, in kilograms"
      },
      "body_fat_percent": {
       "type": "number",
       "description": "Body fat, as a percentage"
      },
      "healthy_range_percent": {
       "type": "string",
  
… (truncated)
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/saylor-innovations-body-fat-calculator-us-navy-method-5796bc52/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from saylorinnovations.com](https://www.zero.xyz/host/saylorinnovations.com/llms.txt)