BMI and Waist-to-Height Ratio Calculator

Calculate BMI and waist-to-height ratio, with NICE lower thresholds for some ethnic groups.

By Dr Amer Sheikh, GP Updated 17 October 2026 Clinical review pending

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BMI categories

BMI (kg/m²)	Category
Below 18.5	Underweight
18.5–24.9	Healthy weight
25–29.9	Overweight
30–39.9	Obesity
40 or more	Severe obesity

NICE uses lower thresholds (23 and 27.5) for people of South Asian, Chinese, other Asian, Middle Eastern, Black African or African-Caribbean family background.

Waist-to-height ratio

Ratio	Central adiposity
Below 0.5	No increased health risk
0.5–0.59	Increased risk
0.6 or more	High risk

NICE advises using it alongside BMI when BMI is under 35. Keep your waist to less than half your height.

Frequently asked questions

What is a healthy waist-to-height ratio?

Below 0.5. Your waist should be less than half your height.

Why are BMI thresholds lower for some ethnic groups?

Health risks rise at lower BMIs in these groups, so NICE uses 23 and 27.5.

When is BMI unreliable?

In high muscle mass, older adults and pregnancy.

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References

NICE. Overweight and obesity management (2025). NG246. nice.org.uk/guidance/ng246

MedToolbox supports, and does not replace, clinical judgement, national guidance and local policy.