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Waist-to-Height Ratio Calculator

Divides waist circumference by height and classifies the ratio using the 'keep your waist to less than half your height' guidance (NICE 2022).

When to use

You want a simple central-adiposity screen that predicts cardiometabolic risk better than BMI alone.

Do not use when: The person is under 18 or pregnant.

Formula

ratio = waist_cm / height_cm

Inputs

Parameter	Type	Unit	Required	Description
`waist_cm`	number	cm	yes	Waist measured midway between the lowest rib and the top of the hip bone. Range: ≥ 30, ≤ 300
`height_cm`	number	cm	yes	Height in centimetres. Range: ≥ 50, ≤ 300

Outputs

Output	Type	Unit	Description
`ratio`	number		waist / height (same units).
`category`	string		Risk band: below 0.4 low/very slim, 0.4–0.49 healthy, 0.5–0.59 increased risk, 0.6 and above high risk.
`max_healthy_waist_cm`	number	cm	Waist circumference at which the ratio would reach 0.5.

Example

Waist 85 cm, height 175 cm: {"waist_cm":85,"height_cm":175} → {"ratio":0.486,"category":"Healthy","max_healthy_waist_cm":87.5}

Waist 100 cm, height 170 cm: {"waist_cm":100,"height_cm":170} → {"ratio":0.588,"category":"Increased risk"}

GET https://tttkmbb.com/api/v1/calculate/waist-to-height-ratio?waist_cm=85&height_cm=175

Machine access

API: GET https://tttkmbb.com/api/v1/calculate/waist-to-height-ratio (query parameters) or POST with a JSON body {"inputs": {...}}
Schema: https://tttkmbb.com/api/v1/calculators/waist-to-height-ratio · Markdown: https://tttkmbb.com/health/waist-to-height-ratio.md · JSON definition: https://tttkmbb.com/health/waist-to-height-ratio.json
MCP: server https://tttkmbb.com/mcp, tool run_calculator with calculator_id="waist-to-height-ratio"
OpenAPI operationId: calculate_waist_to_height_ratio
Freshness: static. Authentication: none. Rate limit: fair use (see rate limits).

Sources

FAQ

Why is 0.5 the threshold?

Meta-analyses show cardiometabolic risk rises clearly once the waist exceeds half the height, across sexes and ethnic groups, which is why NICE adopted it.

Related calculators

BMI Calculator — Combine with BMI for a fuller screening picture.
Body Fat Calculator — Estimate body-fat percentage from circumferences.