Body Mass Index (BMI) is weight in kilograms divided by height in meters squared (kg/m²). The World Health Organization (WHO) uses it as a population-level screening tool for underweight, normal weight, overweight, and obesity.

What are the WHO BMI categories?

For adults, underweight is a BMI below 18.5, normal (healthy) weight is 18.5 to 24.9, overweight is 25 to 29.9, obesity class I is 30 to 34.9, class II is 35 to 39.9 and class III is 40 or higher. These are the WHO cutoffs, and the CDC uses the same ranges for adults 20 and older. The CDC also calls class III severe obesity. Your BMI is rounded to one decimal and the category is read from that number, so 24.96 shows as 25.0 and counts as overweight.

Is BMI the same for men and women?

The standard WHO BMI formula and cutoffs are the same for adult men and women. BMI does not directly measure body fat percentage, so athletes with high muscle mass may be classified as overweight despite being healthy.

BMI is a useful first-pass screening tool but has limitations: it does not account for muscle mass, bone density, age, or fat distribution. It is best used alongside other health indicators and professional medical advice.

What units does this calculator support?

Metric (kilograms and centimeters) and imperial (pounds, feet and inches). Imperial entries are converted to kilograms and meters before BMI is worked out, and the healthy weight range is shown in the unit you picked. Switching units does not convert numbers you already typed, so re-enter your height and weight after you switch.

How is the healthy weight range calculated?

The healthy weight range corresponds to a BMI of 18.5–24.9 for your entered height. The lower bound uses 18.5 × height² and the upper bound uses 24.9 × height².

Can I use this BMI calculator for children or teens?

No. The adult categories apply from age 20 in CDC guidance (18 in WHO guidance). For ages 2 to 19, BMI is compared with children of the same age and sex on growth charts: below the 5th percentile is underweight, the 85th to below the 95th is overweight and the 95th or above is obesity. This calculator does not ask for age or sex, so it only gives adult categories.

Are BMI cutoffs different for Asian adults?

Often, yes. A 2004 WHO expert consultation found higher health risk at lower BMI in many Asian populations and proposed extra action points at 23 and 27.5. In the UK, NICE uses 23 for overweight and 27.5 for obesity in people of South Asian, Chinese, other Asian, Middle Eastern, Black African or African-Caribbean family background. This calculator shows the standard WHO categories only.

What should I check besides BMI?

Waist size, because BMI cannot tell fat from muscle or show where fat sits. NICE advises adults with a BMI under 35 to keep their waist to less than half their height. At 5 ft 9 in (69 in) that means a waist under 34.5 in, and at 175 cm under 87.5 cm. A doctor may also look at blood pressure, blood sugar and cholesterol.

BMI Calculator

Enter your height and weight in metric or imperial units to instantly see your BMI and WHO weight category.

BMI is weight in kilograms divided by height in meters squared, or 703 × weight in pounds ÷ height in inches squared.

Measurements

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Weight

Enter your height and weight to see results.

Results update instantly as you type.

Quick answer

BMI is weight in kilograms divided by height in meters squared, or 703 × weight in pounds ÷ height in inches squared. For adults, under 18.5 is underweight, 18.5 to 24.9 is normal weight, 25 to 29.9 is overweight and 30 or more is obese. Someone 5 ft 9 in and 160 lb has a BMI of 23.6, and 175 cm with 70 kg gives 22.9.

Examples

Height, weight	BMI	Category
5 ft 4 in, 120 lb	20.6	Normal weight
5 ft 9 in, 160 lb	23.6	Normal weight
5 ft 10 in, 185 lb	26.5	Overweight
6 ft 0 in, 230 lb	31.2	Obese Class I
160 cm, 55 kg	21.5	Normal weight
180 cm, 95 kg	29.3	Overweight

Pick Metric or Imperial, then enter your height and weight.

Summary

Enter your height and weight in metric or imperial units to instantly see your BMI and WHO weight category.

How it works

Choose metric (kg/cm) or imperial (lb/ft·in) units.
Enter your height in the height field.
Enter your weight in the weight field.
Your BMI and WHO category appear instantly.
Review the color-coded scale to see where you fall.
Check your healthy weight range for your height.

Use cases

Quickly check whether your weight is in a healthy range.
Switch between metric and imperial units without manual conversion.
Understand your WHO weight category (Underweight through Obese III).
Find your target healthy weight range to guide fitness goals.
Use as a baseline before starting a diet or exercise program.
Share a simple BMI snapshot with a healthcare provider.

Frequently Asked Questions

Last updated: 2026-05-23 · Reviewed by Nham Vu

BMI Calculator

Measurements

WHO BMI Scale

WHO Classification

Quick answer

Examples

Summary

How it works

Use cases

Frequently Asked Questions

BMI Calculator

Use the BMI Calculator

Measurements

WHO BMI Scale

WHO Classification

Quick answer

Examples

Summary

How it works

Use cases

Frequently Asked Questions