BMI Calculator
Calculate your Body Mass Index
About BMI Calculator
Use this BMI calculator to estimate your body mass index from your height and weight. It is a quick way to screen whether your weight is in a typical range for your height. BMI can help you set goals, track progress, and start a conversation with a healthcare professional about overall health.
While BMI is widely used, it does not directly measure body fat. People with more muscle mass or different frame sizes can have a higher BMI without the same health risks. Use BMI as a helpful indicator, not a diagnosis.
Your BMI
22.7
Normal
Under 18.5
Underweight
18.5 - 24.9
Normal
25 - 29.9
Overweight
30+
Obese
What Is BMI?
Body Mass Index (BMI) is a ratio of weight to height that provides a simple estimate of body size. It is commonly used to classify weight categories in adults. BMI is helpful for population-level screening, but it does not account for muscle mass, bone density, or frame size, so it may not reflect individual health on its own.
The imperial formula uses the factor 703 to convert pounds and inches into the same scale as the metric formula. It is a unit conversion constant that adjusts for the difference between pounds/inches and kilograms/meters.
For a more complete picture, consider additional measures such as waist circumference, body fat percentage, and overall fitness. If you have questions about your results, a healthcare professional can help interpret them in context.
| BMI Range | Classification |
|---|---|
| Below 18.5 | Underweight |
| 18.5 - 24.9 | Normal weight |
| 25.0 - 29.9 | Overweight |
| 30.0 and above | Obesity |
The Formula
How to Calculate Manually
Metric (kg, m)
- Measure your weight in kilograms.
- Measure your height in meters (cm ÷ 100).
- Square your height (m × m).
- Divide weight by squared height.
Imperial (lb, in)
- Measure your weight in pounds.
- Measure height in inches (feet × 12 inches).
- Square your height in inches.
- Multiply weight by 703.
- Divide by squared height.
Examples
Metric example: 70kg and 1.75m
BMI = 70 / (1.75 × 1.75) = 70 / 3.0625 = 22.9 (Normal weight)
Metric example: 90kg and 1.80m
BMI = 90 / (1.80 × 1.80) = 90 / 3.24 = 27.8 (Overweight)
Imperial example: 180 lb and 5 ft 10 in (70 in)
BMI = 703 × 180 / (70 × 70) = 703 × 180 / 4900 = 25.8 (Overweight)
Imperial example: 150 lb and 5 ft 6 in (66 in)
BMI = 703 × 150 / (66 × 66) = 703 × 150 / 4356 = 24.2 (Normal weight)
💡 Tips
- •BMI is a screening tool, not a diagnostic tool - consult a healthcare provider for a complete assessment.
- •Athletes may have a high BMI due to muscle mass, not excess fat.
- •BMI categories may not apply equally to all ethnic groups.
- •For children and teens, BMI is assessed differently using age and sex-specific percentiles.
Fun Facts
- •BMI was never meant for individuals: it was created in 1832 by Belgian mathematician Adolphe Quetelet to study populations, not individuals. He called it the "Quetelet Index" and warned against using it for personal health assessments.
- •The athlete paradox: according to BMI, Dwayne "The Rock" Johnson (6'5", 260 lbs, BMI 30.8) is "obese," Tom Brady was "overweight" during his NFL career, and most Olympic athletes fall into overweight/obese categories despite being in peak physical condition.
- •BMI cutoffs vary by ethnicity: the "healthy" range of 18.5-24.9 was based on European populations. Asian health organizations use 18.5-22.9 because Asians have higher disease risks at lower BMIs, showing one formula does not fit all.
- •The height bias problem: BMI uses height squared in the formula, which underestimates obesity in short people and overestimates it in tall people, a flaw mathematicians have pointed out since the 1800s.
- •Insurance companies love BMI: despite its limitations, 95% of health insurance companies use BMI to determine premiums and coverage, meaning your rates might be higher simply because BMI does not account for muscle mass or bone density.