BMI Calculator

BMI: Body mass index, a height-weight screening measure based on your weight compared with your height squared.

BMI category: The adult group your BMI falls into: underweight, healthy weight, overweight, or obesity.

Healthy weight range minimum: The lowest weight at your height that gives a BMI of 18.5.

Healthy weight range maximum: The highest weight at your height that gives a BMI of 24.9.

Healthy weight range at this height: The span from the minimum to maximum healthy-weight cutoff for your height, shown in lb or kg to match your selected unit system.

BMI note: A reminder that BMI is a screening tool and does not measure body fat directly or diagnose health by itself [1].

Mistake: Choosing the wrong Unit system and then entering cm or kg into US fields, or feet and pounds into metric fields.
Fix: Match your numbers to the selected Unit system before you calculate.

Mistake: Typing total inches into Height (inches) while also filling Height (feet) .
Fix: Put only the extra inches in Height (inches) . Example: 5 ft 9 in means 5 in Height (feet) and 9 in Height (inches) .

Mistake: Leaving Weight (pounds) , Weight (kg) , Height (cm) , or height fields blank and expecting the calculator to treat them as zero.
Fix: Enter a real positive number in each required field for the chosen unit mode.

Mistake: Entering decimals in weight without changing Weight entry precision when you want a more exact value.
Fix: Set Weight entry precision to allow decimals if you want to enter values like 160.5 lb or 72.5 kg.

Mistake: Reading BMI category as a full health diagnosis.
Fix: Use BMI and BMI category as screening results, then read the BMI note for context.

Mistake: Treating Healthy weight range at this height as a perfect personal target for everyone.
Fix: Use Healthy weight range minimum and Healthy weight range maximum as adult screening cutoffs, not as a complete judgment of health.

• Adult BMI cutoffs on this page are for ages 20 and older. They are not child or teen BMI percentiles [1].
• BMI is a screening tool, not a diagnosis. Two people can have the same BMI but different body composition or health risks [1].
• The calculator uses only height and weight. It does not account for muscle mass, frame size, pregnancy, edema, or body fat distribution.
• Results depend on correct units and careful measurement. A small height entry error can noticeably change BMI because height is squared in the formula.
• In US mode, Height (inches) should be the extra inches beyond feet. Entering total inches there can distort the result.
• The healthy weight range shown is the standard adult BMI range of 18.5 to 24.9 at your height, so it is a screening range rather than a personalized goal.
• Very small or very large entered heights can produce mathematically valid but unrealistic BMIs; if that happens, recheck the measurements.

How the calculator works

This calculator uses the standard body mass index method. In metric units, BMI is weight in kilograms divided by height in meters squared [1]. In US units, the same idea is used with a standard conversion factor of 703.

BMI = weight_kg / (height_m^2)

BMI = 703 x weight_lb / (height_in_total^2)

height_in_total = 12 x height_ft + height_in

height_m = height_cm / 100

Adult BMI category cutoffs

For adults ages 20 and older, the calculator compares BMI to the standard cutoffs: underweight is below 18.5, healthy weight is 18.5 to 24.9, overweight is 25.0 to 29.9, and obesity is 30.0 or higher [1]. If a BMI lands exactly on 18.5, 25.0, or 30.0, it goes into the category that starts at that boundary.

Healthy weight range at your height

The healthy weight range is built from the adult healthy-weight BMI cutoffs, 18.5 and 24.9. The calculator first uses height in meters, then converts the result to pounds for US output when needed.

weight_kg_min = 18.5 x (height_m^2)

weight_kg_max = 24.9 x (height_m^2)

weight_lb = weight_kg / 0.45359237

Worked example

Example in US units:

if height is 5 feet 9 inches and weight is 160 pounds, total height is 69 inches. BMI = 703 x 160 / 69^2 = about 23.63, which displays as 23.6. That falls in the healthy weight category. The healthy weight range at 69 inches is about 125.3 to 168.6 lb, which may be shown rounded to about 125 to 169 lb for readability.

Rounding and checks

The calculator uses full precision internally, then displays BMI to 1 decimal place. Healthy weight range values are displayed in the same unit system you entered, with sensible rounding for readability. If your result looks extreme, the tool may suggest rechecking measurements, but it does not change the math result.

Assumptions used here

This method assumes standard adult BMI cutoffs and uses only height and weight. It does not estimate body fat percentage, and it does not adjust for age under 20, sex, muscle mass, or medical conditions that can affect body weight or interpretation [1].