Appendicular skeletal muscle mass calculator
This appendicular skeletal muscle mass calculator estimates the combined lean tissue of the arms and legs from body weight in kilograms, standing height in centimetres, biological sex, and age in years.
Run — free
Appendicular skeletal muscle mass, often shortened to ASM or ASMM, is the compartment used in modern sarcopenia definitions because limb muscle is what dual-energy X-ray absorptiometry can isolate cleanly and what relates most directly to grip strength and gait speed. The engine applies the published Wen anthropometric prediction equation, a linear combination of weight, height, sex code, and age that returns ASM in kilograms without bioimpedance electrodes or a scanner. From that estimate it also computes the appendicular skeletal muscle mass index ASMI as ASM divided by height in metres squared, then compares ASMI to EWGSOP2-style low-muscle cut-offs of seven point zero kilograms per square metre for men and five point five for women. A typical check is a seventy-five kilogram man at one hundred seventy-five centimetres and sixty-five years of age, which yields a finite ASM and ASMI under the same coefficients every time. The whole path is offline and deterministic: no network calls, no random sampling, and no date-dependent shortcuts. Use it free in the browser for teaching, fitness logs, and screening worksheets, or call the API at $0.002 per successful request when you need reproducible ASM fixtures in apps, spreadsheets, or research pipelines that must not invent muscle-mass numbers.
How to use it
Enter your values in the form above. The tool checks them before calculating and shows the result on the same page.
Check your inputs
Use the labels and units shown next to each field. If something is missing or outside the allowed range, the page points to the field to fix.
Use it again or automate it
Use the browser tool for individual checks and the API when you need the same capability in an automated workflow.
What you can do with it
Get an answer now
Enter one set of values and see the result without building a spreadsheet or script.
Compare scenarios
Change one value at a time and rerun the calculation to understand what affects the result.
Automate repeated work
Use the API when the same calculation needs to run inside your product or workflow.
FAQ
What does the appendicular skeletal muscle mass calculator cost?
It is free in your browser on this page. Through the API a successful request costs $0.002; invalid inputs are not charged.
Which formula is used?
The Wen anthropometric equation: ASM = 0.193·W + 0.107·H − 4.157·S − 0.037·A − 2.631, with W in kg, H in cm, S = 1 male / 2 female, and A in years. ASMI is ASM divided by height in metres squared.
What does low_muscle_mass mean?
It is true when ASMI is below the EWGSOP2-style cut-off of 7.0 kg/m² for men or 5.5 kg/m² for women. It is a muscle-quantity screening flag only, not a full sarcopenia diagnosis.
What happens if weight or height is zero or negative?
The input is rejected with invalid_input. Weight and height must be strictly positive for a valid appendicular muscle mass estimate.
Does this replace a DXA or BIA scan?
No. Wen is a simple anthropometric estimate from weight, height, sex, and age. Use measured appendicular lean mass and functional tests when clinical accuracy is required.
For developers — API access
Everything on this page is available programmatically. This section is for teams who want to wire it into their own systems; everyone else can just use the tool above.
API endpoint
Prefer to automate it? One authenticated POST creates the task; the result comes back by webhook or a signed link. The same capability also runs here on the web, by email and from Telegram — and soon from our app too.
Call it from your stack
curl -X POST https://api.kit.forhosting.com/health/appendicular-muscle-mass \
-H "Authorization: Bearer $KIT_KEY" \
-H "Content-Type: application/json" \
-d '{"weight":75,"height":175,"sex":"male","age":65}'const res = await fetch("https://api.kit.forhosting.com/health/appendicular-muscle-mass", {
method: "POST",
headers: {
"Authorization": `Bearer ${process.env.KIT_KEY}`,
"Content-Type": "application/json"
},
body: JSON.stringify({
"weight": 75,
"height": 175,
"sex": "male",
"age": 65
})
});
const { task_id } = await res.json();import os, requests
res = requests.post(
"https://api.kit.forhosting.com/health/appendicular-muscle-mass",
headers={"Authorization": f"Bearer {os.environ['KIT_KEY']}"},
json={
"weight": 75,
"height": 175,
"sex": "male",
"age": 65
},
)
task_id = res.json()["task_id"]<?php
$res = file_get_contents("https://api.kit.forhosting.com/health/appendicular-muscle-mass", false, stream_context_create([
"http" => [
"method" => "POST",
"header" => "Authorization: Bearer " . getenv("KIT_KEY") . "\r\nContent-Type: application/json",
"content" => '{"weight":75,"height":175,"sex":"male","age":65}',
],
]));
$task = json_decode($res, true);body := bytes.NewBufferString(`{"weight":75,"height":175,"sex":"male","age":65}`)
req, _ := http.NewRequest("POST", "https://api.kit.forhosting.com/health/appendicular-muscle-mass", body)
req.Header.Set("Authorization", "Bearer "+os.Getenv("KIT_KEY"))
req.Header.Set("Content-Type", "application/json")
res, _ := http.DefaultClient.Do(req)Example request
{
"weight": 75,
"height": 175,
"sex": "male",
"age": 65
}Example response
{
"task_id": "tsk_a1b2c3d4e5f6a1b2c3d4e5f6",
"type": "health.appendicular_muscle_mass",
"status": "queued",
"_links": {
"result": "/tasks/tsk_…/result"
}
}The API is asynchronous: the call returns a task_id immediately and the result arrives by webhook. Polling is capped at 1 req/s per task.
Pricing
Published price — no tokens, no invented credits. A failed task is never charged.
Limits
max_weight_kg | 500 |
max_height_cm | 300 |
min_age | 18 |
max_age | 120 |
Errors
| HTTP | Code | Meaning |
|---|---|---|
401 | unauthorized | Missing or invalid API key. |
402 | insufficient_balance | Your balance doesn't cover the task price. |
404 | unknown_type | That task type doesn't exist. |
429 | rate_limited | Too many requests. Use the webhook instead of polling. |