BMI calculator API: body mass index and WHO category
Body mass index from weight and height in metric (kg, cm) or imperial (lb, in) units, its WHO adult category (underweight, normal weight, overweight, obesity class I-III) and the weight range that counts as normal for that height. For adults; a screening number, not a diagnosis. Use for health, fitness and nutrition apps.
When to use it
- Compute BMI from kg and cm or from pounds and inches
- Get the WHO adult category and the normal weight range for a height
- Add a BMI step to a health or fitness app
Inputs
| Name | Type | Description |
|---|---|---|
weight (required) | number | Weight in kg (or lb with units=imperial) |
height (required) | number | Height in cm (or inches with units=imperial) |
units | string | metric (default) or imperial |
Request
Over HTTP, with a card key from /credits:
curl -H "Authorization: Bearer adt_…" "https://tools.funwords.eu/calc/bmi?weight=70&height=175"Or one of your 25 free calls, no key:
curl "https://tools.funwords.eu/calc/bmi?weight=70&height=175&trial=1"Without a key, the same URL answers 402 Payment Required with x402 and MPP terms, so an agent with a wallet pays per call in USDC (Base, Polygon, Arbitrum or Solana over x402; Base or Tempo over MPP) and retries.
Example result
{
"bmi": 22.9,
"category": "normal weight",
"normalWeightRange": {
"min": 56.7,
"max": 76.3,
"unit": "kg"
},
"note": "WHO adult categories; not a diagnosis."
}From an AI agent (MCP)
Add the MCP server to Claude, Cursor or any MCP client. This tool is calc_bmi, and the first 25 successful calls are free:
https://tools.funwords.eu/mcpQuestions
Is this medical advice?
No. It is a screening number for adults, not a diagnosis.
Which categories are used?
The WHO adult categories, from underweight to obesity class III.
How do I pay?
Each successful call costs $0.01; failed calls are not charged. The first 25 calls are free. Then pay with card credits (from $1; the key goes in an Authorization header or, for clients that can only fetch a URL, as api_key= in the URL) or per call in USDC over x402 or MPP. No account is needed.