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BMI Calculator for Adults — Check Your Body Mass Index

Body mass index (BMI) is a quick way to see whether your weight is in a healthy range for your height. Use the calculator below — nothing you enter is saved or sent anywhere.

Last updated · Written for patients in Ireland

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For adults. A guide only — not a diagnosis. Nothing you enter is saved or sent anywhere.

What your BMI means for adults

  • Under 18.5 — below the healthy range
  • 18.5 to 24.9 — healthy range
  • 25 to 29.9 — above the healthy range
  • 30 and over — in the range commonly described as obesity

Limits of BMI

BMI is a screening guide, not a diagnosis. It does not tell the difference between muscle and fat, and it can be less reliable for very muscular people, older adults, pregnant women and people of different ethnic backgrounds. Waist size, diet, activity, blood pressure and family history all matter too.

It is for adults aged 18 and over. For a child, ask your child’s GP or public health nurse.

What to do with your result

If your BMI is outside the healthy range, or you are worried about your weight or eating, it can help to talk to a doctor. An online GP can listen, look at your overall health and suggest safe next steps.

Frequently asked questions

How do I calculate BMI?

Divide your weight in kilograms by your height in metres squared. The calculator above does this for you.

Is BMI accurate?

It is a useful guide for most adults, but it is not perfect. Your doctor considers it alongside other measures.

What is a healthy BMI in Ireland?

The same ranges are used as in most countries: 18.5 to 24.9 is the healthy range for most adults.

Official sources and further reading

This page is general information for patients in Ireland, not a diagnosis or personal medical advice. If you are worried about your health, speak to a doctor. In an emergency call 112 or 999.

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