Calculate my BMI
Slide to your height and weight to calculate your BMI instantly, then scroll down to see exactly how the number is worked out.
Free online assessment with an Irish doctor-led service. Takes about 2 minutes.
BMI is a screening tool, not a diagnosis. It does not account for muscle mass, and thresholds can differ by ethnicity (for example, health risk can start at a lower BMI in people of South Asian, Chinese or Black African background). Not for under-18s or during pregnancy.
How to calculate your BMI
BMI (body mass index) is your weight in kilograms divided by your height in metres, squared. The calculator above does it as you slide. To do it yourself:
- Measure your height in metres (170 cm is 1.70 m) and your weight in kilograms.
- Multiply your height by itself: 1.70 × 1.70 = 2.89.
- Divide your weight by that number: 82 ÷ 2.89 = 28.4.
- Compare the result with the bands: 18.5–24.9 is healthy, 25–29.9 overweight, 30 or more obesity.
If you know your weight in stone and pounds
Convert first: multiply stone by 14 and add any pounds to get total pounds, then multiply by 0.4536 for kilograms. 13 st 4 lb is 186 lb, which is 84.4 kg. For height, multiply total inches by 0.0254 to get metres: 5′8″ is 68 inches, which is 1.73 m. Or skip the maths and switch the sliders above to stone and feet/inches.
Worked examples
| Height | Weight | BMI | Category |
|---|---|---|---|
| 1.60 m | 60 kg | 23.4 | Healthy weight |
| 1.70 m | 82 kg | 28.4 | Overweight |
| 1.75 m | 95 kg | 31.0 | Obesity (class 1) |
| 1.65 m | 105 kg | 38.6 | Obesity (class 2) |
| 1.80 m | 125 kg | 38.6 | Obesity (class 2) |
Frequently asked questions
What is the BMI formula?
BMI = weight in kg ÷ (height in m × height in m). In imperial units the equivalent is 703 × weight in pounds ÷ (height in inches)².
How do I calculate my BMI in stone and pounds?
Convert to kilograms and metres first (1 stone = 6.35 kg, 1 inch = 2.54 cm), or switch the calculator above to stone and feet/inches and it converts for you.
Can I calculate my BMI without my exact weight?
You can use an estimate, but a small error in weight or height shifts the result, so weigh yourself in the morning without shoes and measure your height against a wall for the most reliable number.
Is the BMI calculation different for men and women?
No. Adults use the same formula and the same WHO bands regardless of sex. Body-fat percentage does differ between men and women, which is one reason BMI is only a screening tool.
Is this calculator suitable for children?
No. It is for adults aged 18 and over. Children and teenagers are assessed on age- and sex-specific growth charts.
Already have your number? See what your BMI means and what to do next, or use the main BMI calculator Ireland page.