How to calculate your BMI

Body mass index from your height and weight — in metric or imperial — plus the healthy range for your height.

BMI (body mass index) is a quick screening number that relates your weight to your height. It's used by health services worldwide to flag potential under- or overweight — though it's a starting point, not a diagnosis, since it can't tell muscle from fat. The Toolsfully BMI calculator gives you the number, your category, and the healthy weight range for your height. Health data is about as personal as data gets, which is why this calculator runs entirely on your device.

Step-by-step

1. Open the BMI calculator. Go to Calculators and select the BMI tab.
2. Pick your units. Choose Metric (cm, kg) or Imperial (ft/in, lb) with the toggle.
3. Enter height and weight. The BMI value, category, and healthy range update instantly as you type.

Tips

• The healthy range is height-specific. The third tile shows the weight span that corresponds to a BMI of 18.5–24.9 for your height — a more actionable number than the index itself.
• Muscle skews it. Athletes often read "overweight" on BMI while being perfectly lean. Waist measurement and body-fat percentage tell a fuller story.
• Track the trend. A single BMI reading matters less than its direction over months.

Frequently asked questions

What do the categories mean?

Under 18.5 is classed as underweight, 18.5–24.9 as a healthy weight, 25–29.9 as overweight, and 30+ as obese — per the World Health Organization's adult ranges.

Is BMI accurate for everyone?

No — it doesn't account for muscle mass, age, sex, or body composition, and adult ranges don't apply to children. Talk to a healthcare provider about what's right for you.

Is my data private?

Yes. The calculation runs in your browser and your measurements never leave your device.