---
title: "Body mass index and healthy weight range"
method: POST
path: "/v1/bmi"
tags: ["Calculators"]
---

# Body mass index and healthy weight range

`POST /v1/bmi`

## Request

- Base URL: `https://api.calculate.co.nz`
- URL: `https://api.calculate.co.nz/v1/bmi`
- Auth: API key in header `X-API-Key`

Calculate BMI and classify it into the standard categories.

Also returns the healthy weight range for the height given, which is
generally more useful than the index itself because it is expressed in
kilograms rather than an abstract number.

BMI is a population screening tool. It does not distinguish muscle from fat,
and it is a poor guide for athletes, pregnant people, children and older
adults. The categories are the WHO adult ones and are not adjusted for
ethnicity, though some NZ guidance uses different cut-offs for Maori,
Pacific and Asian populations.

## Request body

- BMIRequest
  - `weight_kg` number, required: Weight in kilograms
  - `height_m` number, required: Height in metres

## Response `200`

BMI, its category, and the healthy weight range for that height.

- BMIResponse
  - `result` BMIResult, required
    - `bmi` number, required: Body mass index, weight divided by height squared.
    - `category` string, required: Standard classification: Underweight, Healthy weight, Overweight or Obese.
    - `weight_kg` number, required: Weight you sent, in kilograms.
    - `height_m` number, required: Height you sent, in metres.
    - `healthy_weight_min_kg` number, required: Lightest weight in the healthy BMI band at this height.
    - `healthy_weight_max_kg` number, required: Heaviest weight in the healthy BMI band at this height.
  - `disclaimer` string, required: Scope and limits of this calculation.

## Other responses

- `422`: Validation Error

---

[API](https://skmtc.dev/calculate/apis/calculate-co-nz-api.md) · [All operations](https://skmtc.dev/calculate/apis/calculate-co-nz-api/llms.txt) · [OpenAPI document](https://skmtc.dev/calculate/apis/calculate-co-nz-api/revisions/aa59a8e76614?raw)