BMI Calculator
BMI (body mass index) is weight in kilograms divided by height in metres squared. For adults, a BMI from 18.5 to 24.9 is classed as a healthy weight range. BMI is a screening measure, not a diagnosis.
Calculate BMI
BMI Calculator
<18.5 Normal
18.5–24.9 Overweight
25–29.9 Obesity
30+
BMI formulas
Metric: BMI = weight (kg) ÷ height (m)²
Imperial: BMI = 703 × weight (lb) ÷ height (in)²
Example
70 kg and 175 cm: 70 ÷ 1.75² = 70 ÷ 3.0625 = 22.9.
Adult BMI categories
| BMI | Category |
|---|---|
| Below 18.5 | Underweight |
| 18.5–24.9 | Healthy weight |
| 25–29.9 | Overweight |
| 30 or more | Obesity |
These are the standard World Health Organization adult categories. Some health services use lower thresholds for people of South Asian, Chinese, Middle Eastern, Black African or African-Caribbean background, so check your national guidance.
Limitations
BMI doesn’t measure body fat directly or show where fat is carried. It can overestimate in muscular people and underestimate in older adults. It isn’t suitable for children and teenagers (who use age- and sex-specific percentiles) or during pregnancy. Talk to a healthcare professional for advice about your health.
BMI at a glance for one height
For someone 175 cm (5 ft 9 in) tall, the adult categories correspond roughly to these weights:
| Category | Weight range |
|---|---|
| Underweight (below 18.5) | below about 56.7 kg (125 lb) |
| Healthy weight (18.5–24.9) | about 56.7–76.2 kg (125–168 lb) |
| Overweight (25–29.9) | about 76.6–91.6 kg (169–202 lb) |
| Obesity (30 or more) | about 91.9 kg (203 lb) or more |
Calculated as BMI × height² (1.75 m² = 3.0625). Use the calculator for your own height.
Other measures doctors may use
Waist circumference and waist-to-height ratio give an idea of fat around the middle, which BMI can’t show. A common guide is to keep your waist below half your height. A healthcare professional can tell you which measures suit you.
Frequently asked questions
It calculates BMI exactly from the numbers you enter. Whether BMI reflects your health is a separate question; see the limitations above.
Yes. In metric mode you can switch height to feet and inches while entering weight in kg.
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