Calculate Your BMI
BMI (Body Mass Index) is a screening value calculated from height and weight. Adjust the sliders below to see your BMI and which category it falls into.
The BMI Formula
BMI is calculated by dividing weight by the square of height. There are two versions depending on your unit system:
Metric formula
BMI = weight (kg) / [height (m)]^2
Imperial formula
BMI = [weight (lbs) x 703] / [height (inches)]^2
The constant 703 converts the imperial result to the same kg/m^2 scale used by the metric formula. Both formulas produce identical values for the same person.
Examples
Example 1 -- Metric
Input: Height 175 cm, Weight 70 kg
- Height in meters: 1.75 m
- BMI = 70 / (1.75 x 1.75) = 70 / 3.0625 = 22.9
- Category: Normal weight
Example 2 -- Imperial
Input: Height 5 ft 9 in (69 inches), Weight 185 lbs
- BMI = (185 x 703) / (69 x 69) = 130,055 / 4,761 = 27.3
- Category: Overweight
Example 3 -- Edge of a category boundary
Input: Height 160 cm, Weight 47 kg
- BMI = 47 / (1.60 x 1.60) = 47 / 2.56 = 18.4
- Category: Underweight (just below the 18.5 threshold)
What BMI Does and Does Not Measure
BMI is a single number derived from height and weight. It is useful as a quick population-level screening metric, but it has well-documented limitations:
| What BMI measures | What BMI does not measure |
|---|---|
| Weight-to-height ratio | Body fat percentage |
| A general weight category | Muscle vs. fat composition |
| Population-level trends | Bone density or frame size |
| -- | Fat distribution (e.g., visceral vs. subcutaneous) |
| -- | Age, gender, or ethnicity differences |
Because BMI does not distinguish between muscle and fat mass, it can misclassify individuals. A muscular athlete may have a BMI above 25 with low body fat, while an older adult with low muscle mass may have a BMI in the normal range despite higher body fat.
For a more complete picture, other measurements exist -- such as body fat percentage, waist circumference, and waist-to-hip ratio -- though these typically require additional tools or professional measurement.
BMI Across Different Heights
To illustrate how BMI maps to weight at various heights, here are the approximate weight ranges for a "normal" BMI (18.5--24.9):
| Height | Normal BMI range (weight) |
|---|---|
| 155 cm / 5'1" | 44--60 kg / 97--132 lbs |
| 165 cm / 5'5" | 50--68 kg / 111--150 lbs |
| 175 cm / 5'9" | 57--76 kg / 125--169 lbs |
| 185 cm / 6'1" | 63--85 kg / 140--188 lbs |
| 195 cm / 6'5" | 70--95 kg / 155--209 lbs |
Values rounded to the nearest whole number. These ranges are derived directly from the BMI formula, not from health recommendations.
Frequently Asked Questions
What is BMI?
BMI (Body Mass Index) is a numerical value calculated from a person's height and weight. The metric formula is BMI = weight (kg) / height (m)^2. It was developed in the 19th century by mathematician Adolphe Quetelet and is widely used as a general screening tool for categorizing weight status.
How do I calculate BMI?
For metric units: divide your weight in kilograms by your height in meters squared. For imperial units: multiply your weight in pounds by 703, then divide by height in inches squared. Example: 70 kg and 1.75 m -- BMI = 70 / (1.75^2) = 22.9.
What are the BMI categories?
The standard WHO categories for adults are: Underweight (below 18.5), Normal weight (18.5--24.9), Overweight (25.0--29.9), and Obese (30.0 and above). Some guidelines further subdivide the obese category into Class I (30--34.9), Class II (35--39.9), and Class III (40+).
Is BMI accurate for athletes or muscular people?
BMI often overestimates body fatness in muscular individuals because it cannot distinguish muscle from fat. An athlete with significant muscle mass may have a BMI above 25 while having a low body fat percentage. In these cases, body composition measurements provide more meaningful information.
Does BMI apply to children and teenagers?
The BMI formula is the same for children, but the interpretation differs. For ages 2--19, BMI is plotted on age- and sex-specific growth charts and expressed as a percentile rather than using the fixed adult thresholds.
What is a healthy BMI range?
The WHO defines a normal BMI as 18.5 to 24.9 for adults. However, BMI alone does not determine health status. Factors like activity level, diet, genetics, and body composition all play a role. BMI is a starting point, not a complete assessment.
Why is the number 703 used in the imperial BMI formula?
The constant 703 converts the imperial units (pounds and inches) so the result matches the metric BMI scale (kg/m^2). It comes from the unit conversion: 1 kg = 2.20462 lbs and 1 m = 39.3701 inches -- 703 is approximately 2.20462 x 39.3701^2.
Does this calculator store my data?
No. All calculations run entirely in your browser. No data is sent to any server, and nothing is stored.
Related Tools
- Body Fat Calculator -- estimate body fat percentage using additional measurements
- Ideal Weight Calculator -- see ideal weight estimates from multiple formulas
- BMR Calculator -- calculate your basal metabolic rate
- Calorie Needs Calculator -- estimate daily caloric needs based on activity level
- Macro Calculator -- calculate protein, carbs, and fat targets
Privacy & Limitations
Privacy: This calculator runs entirely in your browser. No personal data -- including height, weight, or BMI results -- is transmitted or stored anywhere.
Limitations: BMI is a general screening tool. It does not account for body composition, muscle mass, bone density, age, sex, or ethnicity. It is not a diagnostic measure and should not be used as a substitute for professional medical evaluation.
Related Tools
View all toolsBMR Calculator
Estimate basal metabolic rate (BMR)
Body Fat Calculator
Estimate body fat percentage from BMI
Calorie Needs Calculator
Estimate daily calories by activity level
Ideal Weight Calculator
Estimate ideal weight from height
Pace Calculator
Calculate running pace and race finish times
Calories Burned Calculator
Estimate calories burned from any activity
BMI Calculator FAQ
What is BMI?
BMI (Body Mass Index) is a numerical value calculated from a person's height and weight. The metric formula is BMI = weight (kg) / height (m)². It is used as a general screening tool to categorize weight status into underweight, normal, overweight, and obese ranges.
How do I calculate BMI?
For metric units: divide your weight in kilograms by your height in meters squared. For example, 70 kg and 1.75 m → BMI = 70 / (1.75 × 1.75) = 22.9. For imperial units: multiply your weight in pounds by 703, then divide by your height in inches squared.
What are the BMI categories?
The standard WHO categories are: Underweight (below 18.5), Normal weight (18.5–24.9), Overweight (25–29.9), and Obese (30 and above). These thresholds apply to adults aged 20 and older.
Is BMI accurate for everyone?
No. BMI does not distinguish between muscle and fat, does not account for bone density, age, gender, or body composition, and may misclassify athletes or elderly individuals. It is a population-level screening tool, not a diagnostic measure.
What is the BMI formula?
Metric: BMI = weight (kg) / [height (m)]². Imperial: BMI = [weight (lbs) × 703] / [height (inches)]². Both formulas produce the same result in kg/m² units.
Does BMI apply to children?
For children and teens (ages 2–19), BMI is calculated the same way but interpreted using age- and sex-specific percentile charts rather than the fixed adult thresholds. A pediatric healthcare provider can interpret these percentiles.
Why do athletes sometimes have a high BMI?
Muscle is denser than fat. Because BMI only considers total weight relative to height, people with significant muscle mass — such as athletes or bodybuilders — can have a BMI in the overweight or obese range despite having low body fat.
Does this calculator store my data?
No. All calculations run entirely in your browser. No data is sent to any server, and nothing is stored.