BMI calculator
BMI = weight in kilograms ÷ (height in meters)². For adults, the WHO classes a BMI under 18.5 as underweight, from 25 as overweight and from 30 as obesity.
- Checked on thousands of cases
- Sources: WHO
- Updated November 1, 2026
Your BMI
Normal weight
Normal weight for your height: 119 lb to 159 lb
For adults aged 18 and over. Not suitable for children, pregnant women or very muscular people.
How it works
Formula: BMI = weight (kg) ÷ height² (m²)
Divide your weight in kilograms by the square of your height in meters. For example, 70 kg and 1.75 m give 70 ÷ (1.75 × 1.75) ≈ 22.9. In imperial units, the calculator converts feet, inches and pounds to metric first. BMI is a quick screening measure for adults: it does not distinguish muscle from fat and does not account for age, sex or body shape, so it does not apply to children, pregnant women or very muscular people.
Worked examples
1.7 m and 65 kg
65 ÷ (1.7 × 1.7) = 22.5.
1.8 m and 90 kg
A BMI of 27.8.
5 ft 9 in and 160 lb
After converting to meters and kilos: 23.6.
Common mistakes
Using the height in centimeters: 65 ÷ 170² = 0.0022.
Height goes in meters: 22.5.
Dividing by the height without squaring it.
Divide by height × height.
Using adult cut-offs for a child.
For children, the WHO uses charts by age and sex.
WHO BMI categories for adults
| Category | BMI |
|---|---|
| Underweight | < 18.5 |
| Normal weight | 18.5 – 24.9 |
| Overweight | 25.0 – 29.9 |
| Obesity | ≥ 30.0 |
Normal weight range by height
| Height | Normal weight |
|---|---|
| 4′ 10″ | 89 – 119 lb |
| 5′ 0″ | 95 – 128 lb |
| 5′ 2″ | 102 – 136 lb |
| 5′ 4″ | 108 – 145 lb |
| 5′ 6″ | 115 – 154 lb |
| 5′ 8″ | 122 – 164 lb |
| 5′ 10″ | 129 – 174 lb |
| 6′ 0″ | 137 – 184 lb |
| 6′ 2″ | 145 – 194 lb |
| 6′ 4″ | 152 – 205 lb |
Frequently asked questions
What is a normal BMI?
For adults, the WHO considers a BMI from 18.5 up to (but not including) 25 as normal. Below 18.5 is underweight, from 25 overweight and from 30 obesity.
How do I calculate my BMI by hand?
Multiply your height in meters by itself, then divide your weight in kilograms by the result. 80 kg and 1.80 m: 1.80 × 1.80 = 3.24, and 80 ÷ 3.24 ≈ 24.7.
Does BMI apply to children?
No. For children and teenagers, the WHO uses BMI-for-age charts that depend on age and sex. This calculator is for adults aged 18 and over.
Is BMI a reliable measure?
It is a useful population-level indicator, but limited for individuals: a muscular athlete can have a high BMI without excess fat. Waist size and a health professional's assessment give a fuller picture.