Calculators

BMI Calculator

Enter your height and weight to calculate your Body Mass Index (BMI) and see which weight category you fall into. Supports metric and imperial units.

Calculators · BMI CalculatorRuns in your browser

Height (cm)

Weight (kg)

Your BMI

22.9

How to calculate your BMI

Choose Metric or Imperial. Metric asks for height in centimetres and weight in kilograms; Imperial asks for feet, inches and pounds.
Type your height and weight. Decimals are accepted, so 172.5 cm or 68.4 kg are fine.
Read your BMI to one decimal place, your weight category, and the healthy weight range for your height.
Check the coloured scale and the note under it, which says how far you are from the healthy range.

Every output on the result card

Output	How it is produced	Example
Your BMI	weight ÷ height² (height in metres), shown to 1 decimal	50 ÷ 2.56 = 19.5
Category	WHO bands applied to the unrounded BMI	Healthy weight
Healthy weight range	18.5 × height² to 24.9 × height²	47.4 – 63.7 kg
Scale marker	Position of the BMI between 15 and 40	18% along the bar
Note	Distance to the nearest edge of the healthy range	Within the healthy range

Worked for a person 160 cm tall weighing 50 kg.

Category boundaries exactly as applied

The category is decided on the exact value, not the rounded one. A BMI of 24.96 displays as 25.0 yet is still labelled Healthy weight, and the note about weight to lose or gain follows the same boundaries as the category, so it stays silent across the whole healthy band. At 175 cm and 76.4 kg, BMI 24.95, the category reads Healthy and no amount to lose is shown; at 76.6 kg the category switches to Overweight and the note measures the distance back to the top of the range.

BMI	Category shown
below 18.5	Underweight
18.5 up to, but not including, 25	Healthy weight
25 up to, but not including, 30	Overweight
30 and above	Obese

What the imperial mode does with your numbers

Feet and inches are combined into total inches, so 5 ft 9 in becomes 69 in, and BMI is computed with the 703 factor. The healthy weight range and the amount to lose or gain are converted back to pounds at 0.45359237 kg per lb and shown as whole pounds; for 5 ft 9 in the range is 125 – 169 lb. Entering 5 ft 13 in works and is read as 73 in, and 0 in the inches field is fine as long as the feet field is not also 0.

The two unit modes keep separate fields. Switching from metric to imperial shows the imperial starting values (5 ft 9 in, 154 lb) rather than converting what you typed, so enter your figures again after switching.

Reading the scale bar

The bar runs from BMI 15 at the left edge to 40 at the right, coloured blue below 18.5, green up to 25, amber up to 30 and red beyond. The triangle marks your value, and it is clamped to the ends: a BMI of 12 sits at the far left and a BMI of 45 at the far right, while the number in the box stays exact.

The gain and lose notes

If your weight is above the top of the healthy range, the note shows how far above it you are, measured to the 24.9 limit. If it is below the bottom, it shows how far below the 18.5 limit. A person 160 cm tall at 45 kg has a BMI of 17.6, Underweight, and the bottom of their range is 47.4 kg, so the note reads about 2.4 kg to gain. Metric notes are rounded to 0.1 kg and imperial notes to the nearest pound.

When to treat the result with caution

The bands are for adults. Children and teenagers are assessed with age-and-sex percentiles instead.
During pregnancy BMI is not used for weight assessment.
Over about 65, a slightly higher BMI is often considered acceptable, and the Underweight threshold matters more.
Some health bodies apply lower cut-offs (23 for Overweight, 27.5 for Obese) for people of South Asian, Chinese and some other ancestries, which this tool does not do.
Very short or very tall people get BMI values that are slightly distorted because the formula squares height.

Frequently asked questions

What is a healthy BMI range?

For most adults a BMI between 18.5 and 24.9 is considered healthy. Below 18.5 is underweight, 25–29.9 is overweight and 30+ is obese.

Is BMI accurate for everyone?

BMI is a general guide and does not distinguish muscle from fat. Athletes and very muscular people may get a high BMI despite low body fat.

Why is the range shown as 18.5–24.9 when the category changes at 25?

Both are the standard WHO presentation: the healthy band is written as 18.5 to 24.9 and the next band starts at 25.0. The calculator uses the 25.0 boundary for both the category and the note, so a BMI of 24.95 counts as healthy with nothing to lose.

Can I enter my height in metres?

No, the metric field expects centimetres. Type 175 for 1.75 m. Entering 1.75 would give an absurdly high BMI.

What happens if I leave a field blank or enter 0?

The result card disappears until every required field has a value above 0. In imperial mode the feet and inches are added together, so 0 in one of them is fine as long as the total is not 0.

Is the formula different for men and women?

No. The same calculation and the same category thresholds are used for everyone, which is one reason BMI is only a screening measure. The separate pages for men and women discuss how to interpret the result.

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