What is BMI?

Body mass index, or BMI, is a number that compares your weight with your height. Health organizations use it as a quick screening tool to sort adults into weight categories: underweight, healthy weight, overweight and obesity. A BMI calculator does the math for you in a second, so you can see where your numbers fall.

BMI is easy to find and the same formula works for everyone, which is why doctors, researchers and public health agencies use it. But it is only a screening number. It does not measure body fat directly and it cannot tell you how healthy you are on its own. We explain its limits below.

The BMI formula

• Metric: BMI = weight in kilograms ÷ (height in meters × height in meters).
• US units: BMI = 703 × weight in pounds ÷ (height in inches × height in inches).

For example, a person who is 5 feet 9 inches (69 inches) tall and weighs 160 pounds has a BMI of 703 × 160 ÷ (69 × 69) = 112,480 ÷ 4,761, which is about 23.6. That is in the healthy weight range.

How to use this calculator

1. Choose your units: US (feet, inches, pounds) or metric (centimeters, kilograms).
2. Enter your height and your weight.
3. Press Calculate.
4. Read your BMI, your weight category, and the weight range that matches a BMI of 18.5 to 24.9 for your height.

For the most accurate result, measure your height without shoes and weigh yourself at a consistent time of day.

Adult BMI categories

The U.S. Centers for Disease Control and Prevention (CDC) uses the following categories for adults age 20 and older. The same categories apply regardless of age, sex or race.

BMI (kg/m²)	Category
Less than 18.5	Underweight
18.5 to less than 25	Healthy Weight
25 to less than 30	Overweight
30 or higher	Obesity
30 to less than 35	Class 1 Obesity
35 to less than 40	Class 2 Obesity
40 or higher	Class 3 Obesity (severe obesity)

The CDC gives this example for an adult who is 5 feet 9 inches tall: a weight of 124 pounds or less is underweight, 125 to 168 pounds is in the healthy weight range, 169 to 202 pounds is overweight, and 203 pounds or more is in the obesity range.

Healthy weight range by height

This table shows the weight range that matches a BMI of 18.5 to 24.9 for several heights. It is a general guide, and the calculator above shows the range for your exact height.

Height	Weight range (BMI 18.5 to 24.9)
5 ft 0 in	95 to 128 lb
5 ft 2 in	101 to 136 lb
5 ft 4 in	108 to 145 lb
5 ft 6 in	115 to 154 lb
5 ft 8 in	122 to 164 lb
5 ft 10 in	129 to 174 lb
6 ft 0 in	136 to 184 lb
6 ft 2 in	144 to 194 lb
6 ft 4 in	152 to 205 lb

What BMI does not tell you

• Muscle and fat. BMI treats all weight the same. A muscular person can have a high BMI without having extra body fat.
• Where fat is stored. Fat around the waist carries more health risk than fat on the hips or thighs, and BMI cannot show this.
• Age. Older adults often have less muscle, so they can have a normal BMI and still have more body fat than is ideal.
• Children and teens. This calculator is for adults age 20 and older. Children and teens are measured against growth charts for their age and sex, so please use a children’s BMI tool and ask a pediatrician.
• Pregnancy. BMI is not meant for use during pregnancy.

BMI and waist size

Doctors often look at waist circumference together with BMI. According to National Heart, Lung, and Blood Institute guidance, a waist larger than 40 inches (102 cm) for men or 35 inches (88 cm) for women is linked to higher health risks. For people with a BMI of 35 or more, waist size adds little extra information. If you measure your waist, do it around the middle, just above your hip bones, after breathing out normally.

When to talk to a health care provider

Your BMI is one piece of information. If your BMI is outside the healthy range, or if you have questions about your weight, diet, activity or any health symptoms, a doctor, nurse or registered dietitian can look at the whole picture, including your family history, blood pressure, blood sugar and cholesterol. This page does not give medical advice and cannot diagnose a condition.

Habits that support overall health

• Eat a variety of vegetables, fruit, whole grains, lean proteins and healthy fats.
• Move regularly in ways you enjoy, such as walking, cycling or swimming.
• Get enough sleep, since poor sleep affects appetite and energy.
• Limit sugary drinks and heavily processed foods where you can.
• Make small, steady changes you can keep, rather than extreme ones.

Frequently asked questions

What is a healthy BMI?

For adults, a BMI from 18.5 to less than 25 is in the healthy weight range, according to the CDC.

Is BMI accurate for athletes?

Not always. Because muscle weighs more than fat, a very muscular person may have a BMI in the overweight range without carrying extra body fat. A doctor can use other measures, such as body fat percentage.

Is the BMI the same for men and women?

Yes. The formula and the adult categories are the same for men and women, though men and women often carry body fat differently.

How often should I check my BMI?

There is no need to check often. Weight changes slowly, so checking every few months is plenty if you want to track it.

Is my information saved?

No. All calculations happen in your browser. Your height and weight are never sent to our server or stored.

Worked examples

Example 1 (US units). A person who is 5 feet 4 inches tall (64 inches) and weighs 135 pounds has a BMI of 703 × 135 ÷ (64 × 64) = 94,905 ÷ 4,096, which is about 23.2. That falls in the healthy weight range.

Example 2 (metric). A person who is 180 cm tall (1.80 m) and weighs 95 kg has a BMI of 95 ÷ (1.80 × 1.80) = 95 ÷ 3.24, which is about 29.3. That falls in the overweight range, close to the line for obesity. Because BMI cannot separate muscle from fat, this person’s doctor might also check waist size, blood pressure and blood sugar.

Example 3 (finding a range). For a height of 1.65 m, the healthy range is 18.5 × 1.65 × 1.65 to 24.9 × 1.65 × 1.65, or about 50.4 to 67.8 kg. The calculator above does this step for you and shows the result in pounds or kilograms.

Why a single number can mislead

Weight changes from day to day because of water, food and salt, so one reading is a snapshot rather than a trend. If you track your BMI, use the same scale, the same time of day and similar clothing. A change of a point or two over several months says far more than a change from one morning to the next.

It is also worth remembering that people at the same BMI can have very different health. Fitness, diet, sleep, family history and blood tests all matter. Use your BMI as a conversation starter with a health professional, not as a grade.

Helpful resources

• Adult BMI Categories from the U.S. Centers for Disease Control and Prevention
• Adult BMI categories and example weight ranges from the CDC
• Our Percentage Calculator and Age Calculator

This calculator is for general information only and is not medical advice. It does not diagnose any condition. Talk to a qualified health professional about your health. See our Terms & Disclaimer.