BMI Calculator is a free tool that turns your height and weight into a Body Mass Index with the standard WHO weight band. It accepts metric or imperial units, shows the healthy range for your height, and runs entirely in your browser — personal numbers never leave your device.
How to check your BMI
- Pick Metric (cm, kg) or Imperial (inches, pounds).
- Enter your Height and Weight — the score updates instantly.
- Read your BMI with its band, and the Healthy range weight span for your height.
- Poor sleep skews weight over time, so check your nights with the Sleep Cycle Calculator next.
What the bands actually mean
Below 18.5 is underweight, 18.5–24.9 is the healthy band, 25–29.9 is overweight, and 30 or above is obese. Those cut-offs describe populations, not people: a rugby player can land “overweight” on muscle alone, and a healthy score never clears anyone of all risk. Treat the number as a prompt for a conversation, ideally one that ends with better sleep and a professional opinion rather than a crash diet.
A worked example
At 70 kg and 175 cm the maths is 70 divided by 1.75 squared — about 22.9, comfortably inside the healthy band. The same person in imperial (154 lb, 69 in) converts to the same inputs first, so both unit systems always agree. Nudge the weight to 85 kg and the score crosses 27.8 into overweight: small sustained changes move the number more than any single reading suggests.
Frequently asked questions
How is BMI calculated?
Weight in kilograms divided by height in metres squared. A 70 kg person at 1.75 m scores 70 / (1.75 × 1.75) ≈ 22.9. Imperial inputs are converted first: 1 lb is 0.4536 kg and 1 inch is 2.54 cm.
What counts as a healthy BMI?
The WHO bands are: below 18.5 underweight, 18.5–24.9 healthy weight, 25–29.9 overweight, and 30 or above obese. They screen populations well but say nothing about muscle, bone or where fat sits.
Is BMI medical advice?
No. It is a screening number, not a diagnosis: athletes can score “overweight” from muscle, and a healthy score never rules out a health problem. Talk to a professional about anything that worries you.
Is my weight uploaded anywhere?
No. The numbers never leave the input boxes: everything is calculated in your browser and gone when you close the page.
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