Free Online BMI Calculator
Check your body mass index from height and weight
Your BMI
23.0
Normal weightHealthy weight for your height: 128.9 lbs – 173.5 lbs
| Category | BMI Range |
|---|---|
| Underweight | Below 18.5 |
| Normal weight | 18.5 – 24.9 |
| Overweight | 25.0 – 29.9 |
| Obese (Class I) | 30.0 – 34.9 |
| Obese (Class II) | 35.0 – 39.9 |
| Obese (Class III) | 40.0 and above |
BMI is a screening tool, not a diagnostic measure. Consult a healthcare professional for health assessments.
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Why use BMI Calculator
- Switches between metric (cm/kg) and imperial (feet-inches/lbs) with one toggle -- no unit conversion on your end.
- Visual gauge plots your BMI on the full spectrum, not just a number with a label.
- Shows the exact healthy weight range for your height so you have a target, not a vague category.
How it works
BMI is calculated using the formula: weight (kg) divided by height (m) squared. If you enter imperial units, the tool converts feet and inches to meters and pounds to kilograms before applying the formula. For example, 70 inches becomes 1.778 meters, and 160 pounds becomes 72.57 kilograms, giving a BMI of 72.57 / (1.778 x 1.778) = 22.96. The result is compared against WHO thresholds: below 18.5 is underweight, 18.5-24.9 is normal, 25-29.9 is overweight, and 30+ is obese. The healthy weight range is calculated by solving the BMI formula backwards for BMI values of 18.5 and 24.9 at your height.
About this tool
Plug in your height and weight to see where you land on the BMI scale. The formula is straightforward: weight in kilograms divided by height in meters squared (kg/m²), or weight in pounds times 703 divided by height in inches squared for imperial units. You get a BMI score, the WHO weight category (underweight below 18.5, normal 18.5–24.9, overweight 25–29.9, obese 30+), and a visual gauge. The calculator also works backward from the formula to show the healthy weight range for your specific height, so you walk away with a concrete number to aim for rather than just a label. BMI has real limitations. Muscle weighs more than fat, so a gym regular can score "overweight" with single-digit body fat. It also ignores bone density and fat distribution. Still, it remains the most widely referenced screening metric in clinical settings, and checking it takes about five seconds here.
How to use BMI Calculator
- Enter your height. Type your height in centimeters, or switch to imperial and enter feet and inches.
- Enter your weight. Type your weight in kilograms or pounds.
- Read your results. Your BMI score, WHO category, visual gauge, and healthy weight range appear immediately.
Use cases
- Starting a weight-loss program and need a baseline -- enter 5'11" and 210 lbs, see a BMI of 29.3 (overweight), and know exactly where the "normal" threshold starts for your height.
- Writing a public health paper that requires manually verified BMI calculations -- plug in data points from your study to double-check your spreadsheet formulas against the standard equation.
Frequently Asked Questions
BMI (Body Mass Index) measures body fat based on height and weight. The formula is weight in kilograms divided by height in meters squared (kg/m²). For example, a person who is 1.75 m tall and weighs 70 kg has a BMI of 22.9. In imperial units, multiply weight in pounds by 703, then divide by height in inches squared.
A BMI between 18.5 and 24.9 is considered normal weight by the World Health Organization. Below 18.5 is underweight, 25–29.9 is overweight, and 30 or above is classified as obese. These ranges apply to adults aged 20 and older.
The WHO defines six categories: Underweight (below 18.5), Normal weight (18.5–24.9), Overweight (25–29.9), Obese Class I (30–34.9), Obese Class II (35–39.9), and Obese Class III (40 and above). Each category indicates different levels of weight-related health risk.
Same formula. Women tend to carry more body fat at the same BMI, so providers may interpret results differently, but the math is identical.
BMI does not distinguish between muscle and fat, so athletes or highly muscular people may be classified as overweight despite low body fat. It also does not account for age, bone density, or fat distribution. BMI is a screening tool, not a definitive health diagnosis.
Multiply your weight in pounds by 703, then divide by your height in inches squared. For example: 160 lbs and 70 inches tall = (160 × 703) / (70 × 70) = 22.9 BMI.
A BMI of 30 or above is classified as obese. Obesity is further divided into three classes: Class I (30–34.9), Class II (35–39.9), and Class III (40 and above), also called severe or morbid obesity. Higher classes indicate greater health risk.
Not with the standard adult categories. For ages 2-19, BMI uses age- and sex-specific percentiles. This calculator is designed for adults 20 and older.
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