BMI Calculator: Check Your Body Mass Index
BMI (Body Mass Index) is a screening measure of weight relative to height, calculated as weight in kilograms divided by height in meters squared (kg/m²). This calculator computes your BMI in metric or imperial units and shows your WHO weight category and the healthy weight range for your height.
BMI Calculator: Check Your Body Mass Index
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Formula: BMI = weight (kg) / height (m)^2
Worked example — BMI: 24.3 - Normal Weight | Health Risk: Low
Medical disclaimer: This calculator is provided for educational and informational purposes only and does not constitute medical advice, diagnosis, or treatment. Results are general estimates and may not reflect your individual circumstances. Always consult a qualified healthcare professional before making decisions about your health.
Reviewed for accuracy by Daniel Agrici, Founder & Lead Developer · Editorial policy
How is BMI calculated?
BMI = weight (kg) / height (m)^2
BMI compares body weight with height. In metric units, divide weight in kilograms by height in meters squared. In imperial units, use BMI = [weight in lbs x 703] / [height in inches]^2.
How do you calculate BMI step by step?
Example 1: Normal BMI Calculation
Problem:Calculate BMI for a 35-year-old male who is 5'10" (178 cm) and weighs 170 lbs (77 kg).
Solution:Height in meters = 178 / 100 = 1.78 m Weight in kg = 170 x 0.4536 = 77.1 kg BMI = 77.1 / (1.78)^2 = 24.3 Category: Normal Weight Ideal weight range: about 129 to 173 lbs
Result:BMI: 24.3 - Normal Weight | Health Risk: Low
Example 2: Obese BMI Calculation
Problem:Calculate BMI for a 45-year-old female who is 5'4" (163 cm) and weighs 200 lbs (91 kg).
Solution:Height in meters = 163 / 100 = 1.63 m Weight in kg = 200 x 0.4536 = 90.7 kg BMI = 90.7 / (1.63)^2 = 34.1 Category: Obese Class I (30-34.9) Ideal weight range (BMI 18.5-24.9): about 108 to 146 lbs Weight to lose to reach a BMI of 24.9: about 54 lbs
Result:BMI: 34.1 - Obese Class I | Increased risk of type 2 diabetes and cardiovascular disease
Example 3: Underweight BMI Calculation
Problem:Calculate BMI for a 22-year-old female who is 5'7" (170 cm) and weighs 105 lbs (48 kg).
Solution:Height in meters = 170 / 100 = 1.70 m Weight in kg = 105 x 0.4536 = 47.6 kg BMI = 47.6 / (1.70)^2 = 16.5 Category: Moderate Thinness (WHO: severe thinness is below 16, moderate thinness 16 to 16.9, mild thinness 17 to 18.4) Ideal weight range (BMI 18.5-24.9): about 118 to 159 lbs Weight to gain to reach a BMI of 18.5: about 13 lbs
Result:BMI: 16.5 - Moderate Thinness | Health Risk: High
What else do people ask about BMI?
What is BMI and what does it measure?
BMI, or Body Mass Index, is a screening tool that compares weight and height. It is useful for broad health screening, but it does not directly measure body fat.
What is a healthy BMI range?
For most adults, a BMI from 18.5 to 24.9 is considered a healthy range. Lower values indicate underweight status, while higher values move into overweight and obesity ranges.
What are the limitations of BMI?
BMI does not separate fat from muscle, does not show where body fat is stored, and does not fully account for age, sex, ethnicity, or athletic build. It works best alongside other health measures.
How do I estimate my ideal weight?
A common BMI-based estimate uses the normal BMI range of 18.5 to 24.9 and multiplies those values by your height in meters squared. That gives a practical healthy-weight range for your height.
Is BMI accurate for children?
Adult BMI ranges are not used for children and teens. Younger users need age- and sex-specific BMI percentile charts, which is why child and teen BMI tools are handled separately.
Why does the imperial BMI formula multiply by 703?
The metric definition is kilograms divided by metres squared. Converting pounds to kilograms multiplies by about 0.4536, and converting inches to metres multiplies by 0.0254, so squaring the height introduces a divisor of about 0.000645. Combining the two conversions gives a single factor close to 703. That is why pounds divided by inches squared, multiplied by 703, reproduces the same number as the metric calculation rather than being a separate index.
How are the classes above the overweight threshold divided?
The conventional adult scheme treats 25 as the start of overweight and 30 as the start of obesity, with obesity then split into classes: roughly 30 to 34.9, 35 to 39.9, and 40 and above. The classes exist because risk associations continue to change across that span, so grouping everything above 30 together would hide meaningful differences. They remain population screening bands, not a statement about any one individual.
Why is height squared rather than cubed in the index?
If bodies scaled as perfect geometric solids, mass would grow with the cube of height and the natural index would use height cubed. In practice adult mass across a population rises closer to the square of height, because taller people are not simply scaled-up versions of shorter ones. Quetelet chose the squared exponent because it made the ratio roughly independent of stature. The compromise is imperfect, which is why the index still drifts slightly for very short and very tall adults.
How does BMI compare with waist circumference as a risk marker?
BMI captures total mass relative to stature and says nothing about where tissue sits. Waist circumference targets abdominal and visceral fat, which is the depot most closely linked with metabolic risk. Two people with the same index can differ substantially in waist measurement, and the pair read together is more informative than either alone. Waist measurement has its own error sources, so a consistent measuring position matters.
How much does a small height error move the result?
Because height appears squared in the denominator, the index is roughly twice as sensitive to a proportional error in height as to one in weight. A one percent error in height, which is under two centimetres for most adults, shifts the result by about two percent. Measuring in shoes, or measuring later in the day when spinal discs have compressed slightly, is enough to move a borderline value across a category line.
References
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