BMI Calculator

How do you calculate BMI and read a worked example?

Enter your weight and height to calculate Body Mass Index (BMI), then read the category and weight range for your selected cutoff profile. In Metric (kg / cm), enter 70 in Weight and 175 in Height. The calculation is 70 ÷ (1.75 × 1.75) = 22.857142…, displayed as 22.9. Both Standard and Asian-Pacific classify that displayed result as Normal weight.

The metric formula is BMI = weight in kg ÷ height in metres². Convert centimetres to metres before squaring: entering 1.75 in the centimetre field means 1.75 cm, not 1.75 m. Results update as you type, so no calculate button is needed. The range panel needs only a valid height; the BMI result also needs a positive weight.

What do Standard and Asian-Pacific BMI categories mean?

Standard uses the World Health Organization adult BMI classification. The option labelled Asian-Pacific applies lower overweight and obese thresholds in this calculator. Changing profiles changes the category boundaries and weight range, but leaves the BMI formula and entered measurements unchanged. The table compares the displayed one-decimal bands.

BMI categories used by the two selectable profiles

Category	Standard	Asian-Pacific
Underweight	Below 18.5	Below 18.5
Normal weight	18.5–24.9	18.5–22.9
Overweight	25.0–29.9	23.0–27.4
Obese	30.0 and above	27.5 and above

The WHO Expert Consultation on BMI in Asian populations identified 23 and 27.5 as additional public-health action points while retaining the international classification. The profile here is a specific preset, not a list of every country's clinical criteria. The tool offers four categories; it does not subdivide the obese category into classes. Expand the classification table below the inputs to see the current profile's bands.

Why does rounding matter near a BMI boundary?

The calculator rounds BMI to one decimal for both display and classification. For example, 74.97 kg at 173.2 cm produces a raw BMI of approximately 24.991. It displays as 25.0 and is classified as Overweight under Standard. A calculator that classifies the unrounded value could label the same measurements differently even when both display 25.0.

The coloured gauge is a visual guide spanning BMI 10–45. Values outside that span place the marker at an end of the gauge; the numeric result is not clipped to those limits. Read the number and category rather than treating the marker as an exact measurement. Selecting another profile also changes the coloured band widths.

How is the healthy weight range calculated for your height?

The underlying relationship is weight = BMI × height in metres². This tool adjusts the endpoints to match its rounded BMI categories, then presents weights in tenths of a kilogram or whole pounds. At 170 cm, Standard shows 53.4–72.1 kg; Asian-Pacific shows 53.4–66.3 kg. Directly multiplying 24.9 by 1.70² gives about 72.0 kg, which explains why a simple manual calculation differs slightly.

With 90 kg and 170 cm under Standard, the panel reports about 17.9 kg above the top of the range. With 45 kg at that height, it reports about 8.4 kg below the bottom. A weight classified as normal is reported as within the range. These differences describe the selected screening band; the calculator does not prescribe weight loss, weight gain, a diet or a schedule.

How do feet, inches and automatic unit conversion work?

Imperial (lbs / in) accepts weight in pounds and separates Height into Feet and Inches. Total height is feet × 12 + inches; 5 feet 9 inches means 69 inches. At 154 lb and that height, the tool displays BMI 22.7. Its imperial factor is 0.45359237 ÷ 0.0254², approximately 703.0696, rather than exactly 703.

Switching unit systems converts weight, height and any entered waist measurement. The conversions use 0.45359237 kg per pound and 2.54 cm per inch; converted values retain up to six decimal places. Empty measurements remain empty. Avoid repeatedly switching units when checking a boundary with unusually precise measurements, since converted fields are rounded. For other quantities, use the Unit Converter.

What does the optional waist-to-height ratio show?

Enter Waist (optional) in the length unit currently selected: centimetres for metric or inches for imperial. The formula is waist ÷ height, using matching units. An 80 cm waist at 170 cm gives 0.47 to two decimal places; 90 cm at the same height gives 0.53. The label compares the unrounded ratio with 0.5.

A ratio exactly equal to 0.5 is labelled “at or above 0.5.” Because the number is rounded for display but the comparison is not, a value just below the boundary can display 0.50 while retaining “below 0.5.” This check is separate from BMI: editing waist does not change BMI or its category. An invalid waist shows a message requesting a value greater than 0.

Does BMI account for age, sex, muscle or body fat?

This calculator is designed for adults aged 18 and over. There are no age or sex inputs, so the same weight, height and profile always produce the same BMI category. It does not calculate children's age- and sex-specific growth-chart percentiles. The Age Calculator can calculate age separately, but does not change this tool's interpretation.

BMI cannot distinguish fat from lean mass, and this tool does not measure body fat percentage. Its category and waist ratio are screening information rather than an individual diagnosis. The absence of body-composition inputs matters when interpreting a muscular person's result. A normal category also does not establish overall health; the calculator assesses only the measurements and profile entered.

What stays on your device, and what can you print?

Measurements are held in the current page's state, and BMI, ranges and ratios are computed locally. The calculator has no measurement upload or persistence operation. The copy control copies the displayed BMI and category. Keep any copied result or saved printout according to your own privacy needs.

Print summary opens the browser print dialog once a BMI result is available. The dated summary contains weight, height, cutoff profile, BMI, category, limitations and the entered waist measurement if present. It omits the calculated waist ratio and weight range. Printing produces a record of your inputs and calculation, not a clinical report or a stored account history.