BMI Calculator

Use the free BMI Calculator to instantly find your Body Mass Index and determine whether you are underweight, normal, overweight, or obese. Supports both imperial (lb, ft+in) and metric (kg, cm).

Written & reviewed by the FinanceMaxing Editorial Team · Updated July 21, 2026 · How we calculate

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About the BMI Calculator

The BMI Calculator computes your Body Mass Index — a widely used screening tool that estimates weight status by comparing your weight to your height. It's quick, free, and requires no special equipment, making it one of the most commonly used health metrics by doctors, researchers, and individuals worldwide.

BMI Formulas

Metric:   BMI = weight (kg) ÷ height (m)²
Imperial: BMI = 703 × weight (lb) ÷ height (in)²

BMI Categories (WHO Standard)

  • Underweight: BMI below 18.5 — may indicate malnutrition or other health issues
  • Normal weight: 18.5 to 24.9 — associated with lowest health risk in most populations
  • Overweight: 25 to 29.9 — increased risk of cardiovascular disease and type 2 diabetes
  • Obese Class I: 30 to 34.9 — high risk; lifestyle changes typically recommended
  • Obese Class II: 35 to 39.9 — very high risk; medical intervention often advised
  • Obese Class III: 40 and above — severe/extreme obesity; highest health risk category

Example Calculation

Person: 5'9" (69 in) tall, 154 lb
BMI = 703 × 154 ÷ (69 × 69)
BMI = 108,262 ÷ 4,761 = 22.7 → Normal weight

What BMI Does and Does Not Measure

BMI is a screening tool, not a diagnostic one. It estimates weight status but does not directly measure:

  • Body fat percentage — see the Body Fat Calculator
  • Muscle mass — a highly muscular person may have a high BMI with low fat
  • Bone density — people with denser bones weigh more without added fat
  • Fat distribution — abdominal (visceral) fat carries higher risk than fat in other areas
  • Metabolic health — some people within "normal" BMI range have metabolic disorders

Your Healthy Weight Range

To find the weight range that puts you in the "Normal" BMI category, rearrange the formula:

Lower bound = 18.5 × height(m)²
Upper bound = 24.9 × height(m)²

Example for 5'9" (1.753 m):
Lower = 18.5 × 3.073 = 56.8 kg (125 lb)
Upper = 24.9 × 3.073 = 76.5 kg (168 lb)

Limitations of BMI

  • Athletes and bodybuilders — high muscle mass inflates BMI without excess fat
  • Older adults — natural muscle loss means BMI may underestimate fat at older ages
  • Ethnicity — Asian populations have higher health risk at lower BMI; some guidelines use thresholds of 23 (overweight) and 27.5 (obese) for these groups
  • Pregnancy — BMI is not a useful tool during pregnancy

Despite these limitations, BMI remains a useful first-step screening measure when used alongside other indicators like waist circumference, blood pressure, and blood glucose. For a more complete health picture, pair your BMI with your BMR Calculator estimate and daily calorie needs from the Calorie Calculator.

Frequently Asked Questions

What is BMI and why is it important?

BMI (Body Mass Index) is a numerical value calculated from your height and weight. It's used as a screening tool to categorize weight status — underweight, normal, overweight, or obese — and identify potential health risks associated with being too heavy or too light. It's widely used because it's free, fast, and non-invasive, though it has known limitations.

How do you calculate BMI?

Metric formula: BMI = weight(kg) ÷ height(m)². Imperial formula: BMI = 703 × weight(lb) ÷ height(in)². Example: a person who is 5'9" (69 in) and weighs 170 lb → BMI = 703 × 170 ÷ (69²) = 119,510 ÷ 4,761 = 25.1 (borderline overweight).

What is a healthy BMI range?

According to the World Health Organization (WHO): 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; Obese Class III = 40 and above. A BMI of 18.5–24.9 is generally considered the healthiest range for adults.

What is my healthy weight range based on BMI?

Rearranging the formula: Healthy weight = 18.5 × height(m)² to 24.9 × height(m)². For a person 5'9" tall (1.753 m): lower bound = 18.5 × 1.753² = 56.8 kg (125 lb); upper bound = 24.9 × 1.753² = 76.5 kg (168 lb). Use the calculator to find your personalized range.

Does BMI measure body fat percentage?

No. BMI is a proxy measure, not a direct measurement of body fat. It does not account for muscle mass, bone density, age, or fat distribution. A muscular athlete may register as 'overweight' despite having low body fat. For a more accurate fat measurement, use a body fat calculator or consult a healthcare provider about DEXA scans or hydrostatic weighing.

Does BMI work for both men and women?

Yes — the same BMI formula and WHO thresholds apply to all adults regardless of sex. However, women naturally carry more body fat than men at the same BMI due to hormonal differences, so the health implications may differ slightly. BMI is also less reliable for older adults (who lose muscle mass) and people with high muscle mass.

Is BMI accurate for all ethnicities?

Not always. Research suggests that people of Asian descent may have higher health risks at lower BMI thresholds. Many health organizations recommend an 'overweight' threshold of 23 and 'obese' threshold of 27.5 for Asian populations, compared to 25 and 30 for other groups. Always consider BMI alongside other health indicators.

Does BMI apply to children?

BMI is calculated the same way for children and teens, but it's interpreted differently — using age- and sex-specific percentile charts rather than fixed thresholds. A child at or above the 95th BMI percentile for their age and sex is considered obese. This calculator is designed for adults.