How to Calculate Your BMI (Metric & Imperial Formulas)
Body Mass Index (BMI) is your weight in kilograms divided by your height in meters squared. It takes about ten seconds to calculate with a calculator — or instantly with an app — and it gives you a quick, standardized snapshot of where your weight sits relative to your height.
The BMI formula (metric)
Example: you weigh 70 kg and are 1.75 m tall. Height squared: 1.75 × 1.75 = 3.06. Then 70 ÷ 3.06 = BMI 22.9 — inside the healthy range for most adults.
The BMI formula (imperial: pounds and inches)
Example: you weigh 160 lb and are 5′7″ (67 inches) tall. Height squared: 67 × 67 = 4,489. Then 160 ÷ 4,489 × 703 = BMI 25.1 — just over the healthy-range cutoff.
What your BMI result means
For most adults aged 18–65, BMI results are grouped into these standard categories:
| BMI | Category |
|---|---|
| Below 18.5 | Underweight |
| 18.5 – 24.9 | Healthy weight |
| 25.0 – 29.9 | Overweight |
| 30.0 and above | Obesity |
For a deeper look at each range — and BMI’s important limitations — see our guide to the healthy BMI range and adult BMI chart.
Common mistakes when calculating BMI
- Mixing unit systems. Kilograms go with meters; pounds go with inches (plus the ×703 factor). Mixing them gives nonsense results.
- Using centimeters instead of meters. 175 cm is 1.75 m — forgetting the conversion is the most common metric error.
- Forgetting to square the height. Height is multiplied by itself before dividing.
- Treating one reading as the whole story. A single BMI number matters less than how it trends as your weight changes.
Why tracking BMI over time beats one-off calculations
Your BMI only changes when your weight changes, so recalculating it once in a while and forgetting the result tells you very little. Logged consistently, though, it becomes a clean trend line: you can see when you crossed into a new category, how fast your BMI is moving, and whether your current routine is actually working. Pairing BMI with body measurements and body fat percentage fills in what BMI alone can’t show — like the difference between losing fat and losing muscle.
Skip the math — calculate and track BMI in one tap
BMI Calculator & Body Tracker calculates your BMI instantly in metric or imperial units, shows your category on a clear gauge, and keeps every result in a dated history so you can watch the trend. Free and completely ad-free.