Calculate body fat

Estimate body fat percentage using circumference measurements and the Wilmore and Behnke (1974) anthropometric equations, a field method used when DEXA or hydrostatic weighing is unavailable.

Inputs

The tool uses height, sex, and circumferences (neck, waist, and hip for women; neck and waist for men). Measure at consistent anatomical landmarks—typically at the narrowest waist, widest hip, and mid-neck with the tape horizontal.

How it differs from BMI

Body fat percentage estimates adiposity directly rather than inferring it from weight and height alone. It can better reflect composition changes during strength training when scale weight is stable.

Limitations

Circumference methods assume typical fat distribution and can over- or under-estimate in athletes, older adults, and people with significant visceral fat. Measurement technique (tape tension, time of day, hydration) shifts results by several percentage points. Equations are population averages, not individual diagnostics.

When to use it

Reach for this tool when you need estimate body fat percentage using the US Navy method from body measurements.. It fits quick checks during development, study, paperwork prep, or everyday planning where you want a transparent result without installing desktop software.

Example

With weight 96 kg and height 166 cm, fat returns a numeric estimate.

This skill is available over A2A JSON-RPC and REST. When you already know the skill id and export, call execute directly—no discovery step required.

REST example

curl -sS -X POST https://toolplaza.app/api/helpers/execute \
  -H 'Content-Type: application/json' \
  -d '{"skillId":"body__fat","export":"calculateNavyBodyFatPercent","args":[10,20]}'

A2A JSON-RPC example

Send POST https://toolplaza.app/api/a2a with:

{
  "jsonrpc": "2.0",
  "id": "1",
  "method": "message/send",
  "params": {
    "message": {
      "messageId": "uuid",
      "role": "user",
      "parts": [
        {
          "kind": "text",
          "text": "ignored"
        }
      ]
    },
    "metadata": {
      "toolplaza": {
        "skillId": "body__fat",
        "export": "calculateNavyBodyFatPercent",
        "args": [
          10,
          20
        ]
      }
    }
  }
}

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