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⚖️ Health BMI Calculator
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BMI Calculator

Body Mass Index in imperial or metric — with healthy weight range and goal planner

lbs
ft
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Your BMI
0.0
Normal weight
UnderweightNormalOverweightObese
Healthy weight range—
Weight to lose/gain—
BMI category—
⚕️ Note: BMI is a screening tool, not a diagnostic measure. Consult a healthcare provider for medical advice.
kg
cm
yrs
▾
Your BMI
0.0
Normal weight
UnderweightNormalOverweightObese
Healthy weight range—
Weight to lose/gain—
BMI category—
⚕️ Note: BMI is a screening tool, not a diagnostic measure. Consult a healthcare provider for medical advice.
lbs
ft
in
BMI
Target Weight
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Current BMI—
Weight to change—
Daily calorie deficit— cal/day
Est. time (1 lb/wk)—
Est. time (2 lbs/wk)—
⚕️ Note: BMI is a screening tool, not a diagnostic measure. Consult a healthcare provider for medical advice.

What Is BMI and How Is It Calculated?

Body Mass Index (BMI) is a numerical value derived from a person's height and weight. It was developed in the 1830s by Belgian mathematician Adolphe Quetelet as a statistical tool for studying populations — not as an individual health diagnostic. Despite its origins as a population-level statistic, BMI became widely adopted in clinical practice during the 1970s and 1980s as a quick screening tool for weight-related health risks.

The BMI formula is straightforward: divide your weight in kilograms by the square of your height in meters. In imperial units used in the United States, the formula is: BMI = (weight in lbs ÷ height in inches²) × 703. The multiplier 703 converts the result from the imperial unit system to match the metric BMI scale.

Worked example: A person weighing 170 lbs standing 5'10" (70 inches) tall: BMI = (170 ÷ 70²) × 703 = (170 ÷ 4,900) × 703 = 0.03469 × 703 = 24.4. This places them in the Normal weight category, near the upper end of the healthy range.

In metric: a person weighing 77 kg at 175 cm (1.75 m): BMI = 77 ÷ (1.75)² = 77 ÷ 3.0625 = 25.1 — just into the Overweight category.

BMI Categories and What They Mean

The World Health Organization (WHO) and the National Institutes of Health (NIH) use the following classification system for adults 20 and older:

BMI RangeCategoryHealth Risk
Below 18.5UnderweightNutritional deficiency, osteoporosis, immune weakness
18.5 – 24.9Normal weightLowest risk for weight-related disease
25.0 – 29.9OverweightIncreased risk for type 2 diabetes, hypertension
30.0 – 34.9Obese Class IHigh risk — lifestyle intervention recommended
35.0 – 39.9Obese Class IIVery high risk — medical management often needed
40.0 and aboveExtreme Obesity (Class III)Severely elevated risk for all metabolic conditions

For children and teenagers (ages 2–19), BMI is interpreted using age- and sex-specific percentile charts because healthy BMI changes significantly with age and developmental stage.

Limitations of BMI as a Health Measure

BMI is a convenient screening tool, but it has well-documented limitations that every user should understand:

  • Muscle mass: BMI cannot distinguish between fat and muscle. A 200 lb bodybuilder with 8% body fat will register as "obese" by BMI while being extremely healthy. Conversely, a sedentary person with a "normal" BMI may still have unhealthy levels of visceral (belly) fat.
  • Fat distribution: Where you carry fat matters as much as how much you carry. Visceral fat around the abdomen (measured by waist circumference) carries significantly higher cardiovascular risk than subcutaneous fat around the hips and thighs.
  • Age: As we age, muscle mass naturally decreases and fat mass increases. An older adult with a "normal" BMI may have a higher proportion of body fat than a younger person at the same BMI.
  • Ethnicity: Research shows that people of Asian descent face elevated health risks at lower BMI thresholds. Some health organizations recommend lower cutoffs (23+ for overweight, 27.5+ for obese) for Asian populations.
  • Sex: Women naturally carry more body fat than men at the same BMI due to hormonal and physiological differences. The single threshold system may misclassify some women as overweight when their body fat percentage is healthy.

Healthy Weight Range by Height

The following table shows the healthy weight range (BMI 18.5–24.9) for common heights in imperial units:

HeightMin Weight (lbs)Max Weight (lbs)
5'0"94 lbs127 lbs
5'2"101 lbs136 lbs
5'4"108 lbs145 lbs
5'6"115 lbs154 lbs
5'8"122 lbs164 lbs
5'10"129 lbs174 lbs
6'0"137 lbs184 lbs
6'2"144 lbs194 lbs

Remember that these ranges represent statistical averages. An athlete at 180 lbs and 5'10" may have perfect health metrics despite being at the "overweight" boundary. Always consult a healthcare provider for a comprehensive health assessment.

Frequently Asked Questions

What is a healthy BMI range? ▼
A healthy BMI range is 18.5 to 24.9. BMI below 18.5 is considered underweight, 25.0–29.9 is overweight, and 30.0 or above is classified as obese. These thresholds apply to adults and are the same for both men and women, though BMI has limitations and should be interpreted alongside other health indicators.
How is BMI calculated? ▼
BMI is calculated by dividing your weight by the square of your height. In metric: BMI = weight(kg) ÷ height(m)². In imperial: BMI = (weight(lbs) ÷ height(in)²) × 703. For example, a person weighing 170 lbs at 5'10" has a BMI of (170 ÷ 4900) × 703 = 24.4, which falls in the Normal weight category.
Is BMI accurate for athletes and muscular people? ▼
No, BMI is not accurate for highly muscular individuals. Since muscle is denser than fat, athletes often have a high BMI despite having very low body fat. A 200 lb linebacker may have a BMI of 30+ (classified as obese) while having 8% body fat. For athletes, body composition measurements like DEXA scans or hydrostatic weighing are more appropriate tools.
What are the limitations of BMI as a health measure? ▼
BMI does not distinguish between fat mass and muscle mass, does not account for fat distribution (where fat is stored matters for health risk), and does not reflect differences in age, sex, or ethnicity. Older adults naturally lose muscle and gain fat, so their BMI may underestimate health risk. People of Asian descent may face elevated health risks at lower BMI thresholds (around 23+).
What BMI is considered obese? ▼
A BMI of 30.0 or higher is classified as obese. Obesity is further divided into three classes: Class I (30.0–34.9), Class II (35.0–39.9), and Class III or Extreme Obesity (40.0 and above). Class III obesity carries significantly elevated risk for type 2 diabetes, cardiovascular disease, sleep apnea, and other serious health conditions.
How can I lower my BMI? ▼
Lowering BMI requires creating a calorie deficit — consuming fewer calories than you burn. A deficit of 500 calories/day leads to approximately 1 lb of weight loss per week. The most sustainable approach combines moderate caloric restriction with regular physical activity. Resistance training helps preserve muscle mass during weight loss, which keeps metabolism higher.
Does BMI differ for men and women? ▼
The BMI formula and category thresholds are the same for men and women. However, healthy body fat percentage differs significantly: 18–24% is healthy for women, while 14–17% is healthy for men. Because women naturally carry more fat at the same BMI, some researchers argue that women's "healthy" BMI range should extend slightly higher, though standard clinical guidelines use the same thresholds.
What is the BMI formula in imperial vs metric units? ▼
Metric formula: BMI = weight in kilograms ÷ (height in meters)². Example: 70 kg ÷ (1.75)² = 22.9. Imperial formula: BMI = (weight in pounds ÷ (height in inches)²) × 703. Example: (170 lbs ÷ (70 inches)²) × 703 = (170 ÷ 4900) × 703 = 24.4. Both formulas produce the same result when units are properly converted.
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