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BMI Calculator

Calculate your Body Mass Index from your height and weight, see which WHO weight category you fall into, and find the healthy weight range for your height — in metric or imperial units.

Understanding the BMI Calculator

The BMI Calculator works out your Body Mass Index from your height and weight in either metric (cm, kg) or imperial (feet/inches, lb) units. It instantly shows your BMI to one decimal place, places you in the World Health Organization weight category — Underweight, Normal, Overweight, or Obese — with a colored indicator, and calculates the healthy weight range for your specific height. Everything runs privately in your browser with nothing sent to a server. BMI is a quick, widely used screening number, but it doesn't measure body fat directly, so treat the result as a general guide rather than a diagnosis and discuss any concerns with a healthcare professional.

How it works

Choose your unit system, then enter your height and weight. In metric, BMI is your weight in kilograms divided by your height in metres squared. In imperial, the tool multiplies weight in pounds by 703 and divides by height in inches squared (feet are converted to inches first by multiplying by 12 and adding the spare inches). The result is matched against the WHO cut-offs: under 18.5 is Underweight, 18.5–24.9 is Normal, 25–29.9 is Overweight, and 30 or above is Obese. The healthy weight range is found by multiplying 18.5 and 24.9 by your height in metres squared, then converting back to pounds for imperial.

Metric: BMI = weight(kg) / height(m)². Imperial: BMI = 703 × weight(lb) / height(in)². Healthy weight range = 18.5 × height(m)² (lower) to 24.9 × height(m)² (upper).

Worked example

Suppose you are 175 cm tall and weigh 70 kg. Convert height to metres: 1.75 m. Square it: 1.75 × 1.75 = 3.0625. Divide weight by that: 70 / 3.0625 = 22.9. A BMI of 22.9 falls in the Normal (18.5–24.9) category. The healthy weight range for 1.75 m is 18.5 × 3.0625 = 56.7 kg up to 24.9 × 3.0625 = 76.3 kg, so at 70 kg you sit comfortably inside the healthy range.

Tips & common mistakes

  • BMI is a screening tool, not a diagnosis — it ignores muscle, bone, and fat distribution, so pair it with other measures like waist circumference.
  • Very muscular people (athletes, weightlifters) often read as Overweight or Obese despite low body fat; don't rely on BMI alone.
  • The standard adult formula is identical for men and women, though average body composition differs at the same BMI.
  • Adult BMI categories don't apply to children and teens, who use age- and sex-specific percentile charts instead.
  • Measure height without shoes and weigh yourself at a consistent time of day for the most reliable number.
  • Use the healthy weight range as a realistic target band rather than fixating on a single ideal number.

Sources & methodology

  • • World Health Organization — Body mass index (BMI) classification
  • • U.S. Centers for Disease Control and Prevention (CDC) — About Adult BMI

Related tools

TDEE CalculatorCalculate your daily calorie needs (TDEE) and BMR from age, weight, height, and activity.Macro CalculatorSplit your daily calories into protein, carbs, and fat for your goal.Body Fat CalculatorEstimate your body fat percentage using the U.S. Navy method from a few body measurements.Ideal Weight CalculatorFind your ideal body weight range for your height using the Devine, Robinson, and BMI methods.

Reviewed by the TopOpenTools editorial team · Last updated June 2026. These tools provide general estimates for educational purposes only and are not financial, tax, insurance, investment, or medical advice. Verify important decisions with a qualified professional.

How to Use This Calculator

  1. 1Pick Metric or Imperial units to match how you measure.
  2. 2Enter your height and weight, then click Calculate BMI.
  3. 3Read your BMI, category, and healthy range — then check daily needs with the TDEE calculator.

Frequently Asked Questions

What is a healthy BMI?

For most adults, a BMI between 18.5 and 24.9 is considered the healthy weight range. Below 18.5 is underweight, 25–29.9 is overweight, and 30 or above is classed as obese.

Is BMI accurate for athletes?

Not always. BMI only uses height and weight, so it can overestimate body fat in very muscular people — many athletes register as "overweight" despite low body fat. Use it as a general screen, not a diagnosis.

Does BMI differ for men and women?

The standard adult BMI formula is identical for men and women. On average women carry more body fat at the same BMI, so the number may be interpreted slightly differently, but the calculation does not change.