BMI Calculator
Work out your body mass index (BMI) from your height and weight. See which weight category you fall into and the healthy weight range for your height — in metric or imperial units.
How to use it
Enter your height and weight using whichever unit system you prefer — the calculator converts for you. It returns your BMI, the category it falls in, and the weight range that would put you in the healthy band for your height.
A worked example
Someone who is 175 cm (5′9″) and weighs 70 kg (154 lb) has a BMI of 22.9, which sits in the healthy range. For that height, a BMI of 18.5–24.9 corresponds to roughly 56.7–76.3 kg (125–168 lb) — so this person could gain or lose several kilograms and still be in the healthy band. BMI is the same calculation in any units: weight in kilograms ÷ height in metres squared, or 703 × pounds ÷ inches².
BMI categories for adults
The World Health Organization uses these standard bands for adults (they don’t apply to children, who are assessed on age-and-sex percentiles):
| BMI | Category |
|---|---|
| Below 18.5 | Underweight |
| 18.5 – 24.9 | Healthy weight |
| 25.0 – 29.9 | Overweight |
| 30.0 and above | Obesity |
Limitations & tips
BMI’s biggest weakness is that it measures total weight, not body composition: it doesn’t directly measure body fat, where that fat sits, or how much of your weight is muscle and bone. A lean, heavily muscled athlete can land in the “overweight” band, while someone with low muscle mass can read “healthy” yet carry excess fat. It also says nothing about fat distribution — and abdominal fat carries more health risk than fat on the hips and thighs.
For a fuller picture, pair BMI with measures that capture composition and shape, such as a body fat estimate or a waist-to-hip ratio. Older adults, who tend to lose muscle, and pregnant or breastfeeding people are also poorly served by standard BMI bands. Use BMI to spot a trend over time rather than to judge a single day, and bring any concerns to a healthcare professional who can interpret the number in context.
Frequently asked questions
How is BMI calculated?
BMI is your weight in kilograms divided by the square of your height in metres (kg/m²). In imperial units it's 703 × pounds ÷ inches². This calculator does the unit conversion for you.
What is a healthy BMI?
For most adults, 18.5–24.9 is considered a healthy weight, below 18.5 is underweight, 25–29.9 is overweight, and 30 or above is obesity. These bands are general guidance and don't apply to children.
Is BMI accurate for everyone?
BMI is a screening tool, not a diagnosis. It doesn't distinguish muscle from fat, so athletes can read high, and it isn't suitable for children, pregnancy, or some populations. Use it alongside other measures and professional advice.
Is BMI different for men and women?
The BMI formula and the standard adult categories are the same for men and women. However, at the same BMI women tend to carry more body fat and men more muscle, so BMI alone can read differently in practice. For a fuller picture, pair it with a body fat estimate or a waist-to-hip ratio.
Do the cut-offs differ for Asian populations?
Yes. The WHO notes that some Asian populations face higher health risk at a lower BMI, and several guidelines treat 23 and above as increased risk and 27.5 and above as high risk, rather than the standard 25/30 thresholds. If this applies to you, interpret your number against those lower cut-offs and consult a local guideline.
What should I do with my BMI number?
Use it as a prompt, not a verdict. If you’re outside the healthy band, small sustainable changes to diet and activity matter more than any single number. The calorie calculator can show your daily energy needs and a sensible target to lose or gain weight gradually. For any health decision, speak with a qualified professional.
Sources & references
- CDC — Adult BMI Categories — the four standard adult BMI bands (underweight, healthy weight, overweight, obesity) used in this tool.
- World Health Organization — Obesity and overweight — the global overweight (BMI ≥25) and obesity (BMI ≥30) thresholds this calculator's categories are based on.
Last updated: July 2026 · How we calculate
BriskToolbox provides estimates for general information only and is not medical advice. Talk to a healthcare professional about your individual health.