BMI Calculator

Calculate your Body Mass Index — free, no signup

What is BMI?

Body Mass Index (BMI) is a numerical value derived from your height and weight. It is the most widely used screening tool to categorize individuals into underweight, normal weight, overweight, or obese ranges. BMI is calculated as weight (kg) divided by height (m) squared — or, in imperial units, weight (lbs) ÷ height (in)² × 703.

BMI is a population-level screening tool, not a diagnostic measure. It does not account for muscle mass, bone density, age, or fat distribution. Athletes with high muscle mass may have high BMIs without elevated health risks, while older adults may have normal BMIs with excess body fat.

How to Calculate BMI

  1. 1

    Select your unit system

    Choose Metric (centimeters and kilograms) or Imperial (feet, inches, and pounds). The calculator handles the conversion automatically.

  2. 2

    Enter your height

    In metric mode, enter your height in centimeters. In imperial mode, enter feet and inches separately.

  3. 3

    Enter your weight

    Enter your weight in kilograms (metric) or pounds (imperial).

  4. 4

    Click Calculate BMI

    Your BMI is displayed instantly with your category (Underweight, Normal, Overweight, or Obese) highlighted on the scale.

BMI Categories (WHO Standard)

Underweight

BMI below 18.5

Associated with nutritional deficiency, weakened immune system, and increased risk of osteoporosis.

Normal weight

BMI 18.5 – 24.9

Associated with the lowest risk of weight-related health conditions. Aim to maintain through balanced diet and exercise.

Overweight

BMI 25.0 – 29.9

Associated with increased risk of heart disease, type 2 diabetes, and high blood pressure.

Obese

BMI 30.0 and above

Associated with significantly elevated risk of cardiovascular disease, diabetes, and certain cancers. Consult a healthcare provider.

Frequently Asked Questions

Is BMI accurate?
BMI is a useful population-level screening tool but has limitations. It overestimates body fat in muscular individuals (athletes, bodybuilders) and underestimates it in older adults who have lost muscle mass. Use BMI alongside other measures like waist circumference and body composition.
What is a healthy BMI for adults?
For most adults aged 18–65, a BMI between 18.5 and 24.9 is considered healthy. For adults over 65, a slightly higher BMI (25–27) may be associated with better health outcomes.
Does BMI differ by age or gender?
The standard adult BMI scale applies to both men and women aged 18+. For children and teens, separate age- and sex-specific BMI percentile charts are used. BMI does not distinguish between men and women despite differences in body composition.
How can I lower my BMI?
BMI decreases when you reduce body weight through a calorie-controlled diet and increased physical activity. Aim for gradual weight loss of 0.5–1 kg per week. Consult a healthcare provider or registered dietitian for a personalized plan.
What is the formula for BMI?
Metric: BMI = weight(kg) ÷ height(m)². Imperial: BMI = (weight(lbs) ÷ height(in)²) × 703.

BMI Quick Reference

A BMI of 22 is often cited as the statistical optimum for longevity. BMI does not measure body fat percentage directly — a DEXA scan, hydrostatic weighing, or bioelectrical impedance analysis provides more precise body composition data.

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