Body measurements

POST /v1/body/measurements · $0.001 a call

Send height, waist and neck (and hip for women), in inches or centimeters. Body fat comes from the US Navy circumference formula, with fat and lean mass when you add weight. BMI, waist to height and waist to hip ratios each come with a category. No photo and no model: the same numbers always give the same answer.

For fitness trackers, coaching apps, weight loss programs.

Request

Send these fields as a JSON body (or form fields) on POST /v1/body/measurements. No photo is needed.

Field	Type	Description
`sex`	one of male, female, required	Picks the formula and the category bands.
`units`	one of in, cm	Units of height, waist, neck and hip. Defaults to in.
`height`	number, 20 to 250, required	Height, without shoes.
`waist`	number, 10 to 250, required	Waist: at the navel for men, at the narrowest point for women.
`neck`	number, 5 to 80, required	Neck, just below the larynx.
`hip`	number, 10 to 250	Hip at the widest point. Required for women, optional for men (adds the waist to hip ratio).
`weight_kg`	number, 25 to 350	Weight in kg. Adds BMI and fat and lean mass.

Photo tips. No photo needed. Measure with a soft tape, snug but not tight, after breathing out normally.

1curl https://truelens.keronlabs.com/v1/body/measurements \
2  -H "Authorization: Bearer $TRUELENS_KEY" \
3  -H "Content-Type: application/json" \
4  -d '{"sex":"male","height":70,"waist":34,"neck":15}'

Response

Field	Description
`summary`	One line, e.g. "Body fat 17.5% (fit), waist to height 0.49 (healthy)".
`body_fat`	percent, category (essential, athletic, fit, average, high), method, fat_mass_kg and lean_mass_kg (null without weight).
`bmi`	value and category, or null without weight_kg.
`waist_to_height`	ratio and category (low, healthy, increased risk, high risk).
`waist_to_hip`	ratio and category, or null without hip.
`notes`	How to measure, and what to read into the numbers.

Example

Output of this API’s own code on the sample request above.

1{
2  "metadata": {
3    "id": "req_9cf4da08fe7f40dab71a",
4    "engine": "body/measurements",
5    "status": "success",
6    "cached": false,
7    "credits_used": 0.1,
8    "created_at": "2026-10-19T09:30:00.000Z",
9    "processing_ms": 40
10  },
11  "summary": "Body fat 17.5% (fit), waist to height 0.49 (healthy)",
12  "units": "in",
13  "body_fat": {
14    "percent": 17.5,
15    "category": "fit",
16    "method": "navy_circumference",
17    "fat_mass_kg": null,
18    "lean_mass_kg": null
19  },
20  "bmi": null,
21  "waist_to_height": {
22    "ratio": 0.49,
23    "category": "healthy"
24  },
25  "waist_to_hip": null,
26  "notes": [
27    "Measure the waist at the navel for men and at the narrowest point for women, relaxed, not sucked in.",
28    "Add hip to get the waist to hip ratio.",
29    "Add weight_kg to get BMI and fat and lean mass."
30  ],
31  "disclaimer": "Tape based estimates, usually within 3 to 4 percentage points of a lab scan. Not a medical assessment."
32}