How to Calculate BMI: The Formula in kg and lbs
To calculate BMI in metric, divide your weight in kilograms by your height in metres squared: BMI = kg ÷ m². In imperial units, divide weight in pounds by height in inches squared, then multiply by 703: BMI = (lb ÷ in²) × 703. Both give the same result.
The BMI Formula in Metric (kg and cm)
The metric BMI formula is the original one, and it is simple:
BMI = weight (kg) ÷ height (m)²
The one thing people trip over is that height goes in metres, not centimetres, and it is squared. So if you are 175 cm tall, that is 1.75 m, and you square it to get 3.0625.
Worked example: someone who weighs 70 kg and is 1.75 m tall. Height squared is 1.75 × 1.75 = 3.0625. Then 70 ÷ 3.0625 = 22.9. A BMI of 22.9 sits comfortably in the healthy range of 18.5 to 24.9.
Second example: 90 kg at 1.80 m. Height squared is 3.24. Then 90 ÷ 3.24 = 27.8, which falls in the overweight band (25 to 29.9). Working through a couple of examples like this makes the formula stick.
The BMI Formula in Imperial (lb and inches)
If you think in pounds and inches, use the imperial version:
BMI = (weight in pounds ÷ height in inches²) × 703
The 703 is a conversion factor that makes the imperial result match the metric one. As with metric, height must be squared, and it is measured in total inches (so 5 feet 9 inches is 69 inches).
Worked example: someone who weighs 154 lb and is 69 inches tall (5'9"). Height squared is 69 × 69 = 4,761. Then 154 ÷ 4,761 = 0.03234, and 0.03234 × 703 = 22.7 — the healthy range, and essentially the same as the metric example above, as it should be.
Second example: 200 lb at 71 inches (5'11"). Height squared is 5,041. Then 200 ÷ 5,041 × 703 = 27.9, in the overweight band. Whichever unit system you prefer, BMI describes the same thing — the app supports both so you never have to convert.
Or Let the App Do It in Five Seconds
Doing the arithmetic by hand is a good way to understand what BMI means, but it is easy to make a slip — forgetting to square the height, or mixing centimetres with metres. The app removes that risk entirely. Open the BMI tab, dial in your height and weight (in kg/cm or lb/in), and your BMI appears instantly, in under five seconds, with no formula to remember.
Beyond the raw number, the app also does the parts that are tedious by hand: it places you in the correct WHO category, shows the healthy weight range for your height, estimates your body fat percentage with the Deurenberg formula, and — on the BMR tab — calculates your daily calorie needs. Because there is no account and no server, every calculation happens privately on your device.
This guide is for general information only and is not medical advice — please consult a doctor or qualified professional about your results.
How to Calculate BMI with the App
Open the BMI tab and pick metric (kg/cm) or imperial (lb/in). You never have to convert between systems by hand.
Dial in your height and weight. The app remembers your last values, so repeat check-ins take only a second.
Your BMI appears instantly, in under five seconds, with no squaring, dividing or multiplying by 703 required.
See your WHO category, the healthy weight range for your height, and an estimated body fat percentage alongside the number.
What is the BMI formula?
In metric, BMI equals weight in kilograms divided by height in metres squared (kg ÷ m²). In imperial, it is weight in pounds divided by height in inches squared, multiplied by 703. Both formulas give the same BMI value for the same person.
Why do I multiply by 703 in the imperial formula?
The 703 is a unit-conversion factor. It scales the pounds-and-inches result so it matches the metric kg-and-metres result. Without it, the imperial number would be far too small. You only use 703 with pounds and inches, never with kilograms and metres.
Do I use my height in centimetres or metres?
For the metric formula, convert to metres first — 175 cm becomes 1.75 m — then square it. Using centimetres directly gives a wildly wrong answer. The app handles this automatically, so you can enter your height in centimetres and still get the correct BMI.
Know Your Numbers, Privately
Download BMI Calculator BMR TDEE Track free and get your BMI, healthy weight range, BMR, TDEE and body fat estimate in seconds. No account, on-device, with private iCloud sync. This app provides general health information, not medical advice.
What Is a Healthy BMI?
The healthy adult BMI range is 18.5 to 24.9 — and it is the same for women and men. See the WHO chart and where BMI has its limits.
Read guideBMR & TDEE: How Many Calories a Day?
The Mifflin-St Jeor formula, five activity multipliers, and the difference between maintenance and a moderate deficit — explained clearly.
Read guideWhat's Your Ideal Weight?
There is no single perfect number — there is a healthy weight range for your height. See an example table for 160, 170 and 180 cm.
Read guideEstimate Your Body Fat Percentage
The app estimates body fat with the Deurenberg formula from your BMI, age and sex — a useful guide, honestly explained against methods like DEXA.
Read guide