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BMI Calculator

This BMI calculator works out your body mass index from your height and weight, shows which CDC weight category it falls in, and gives the weight range that counts as a healthy BMI for your height. It's for adults 20 and older.

Units
Height

Result

BMI 24.3: Healthy weight

BMI24.3
Category (CDC, adults 20+)Healthy weight
Healthy weight for your height122 lb – 164 lb

BMI is a screening measure, not a diagnosis. Categories apply to adults 20 and older.

What Is BMI?

Body mass index (BMI) compares your weight with your height. It’s a quick screening number that health professionals use to put adult weight into broad categories. It isn’t a measure of body fat or a diagnosis, but it’s useful as a starting point.

How to Calculate BMI by Hand

Metric

BMI = weight (kg) ÷ height (m)²

US units

BMI = 703 × weight (lb) ÷ height (in)²

The 703 converts pounds and inches into the metric formula’s units, so both give the same answer.

Worked example

Take an adult who is 5 ft 8 in tall and weighs 160 lb:

  • Height in inches: 5 × 12 + 8 = 68 in
  • Height squared: 68 × 68 = 4,624
  • BMI: 703 × 160 ÷ 4,624 = 24.3

A BMI of 24.3 falls in the CDC’s healthy weight range (18.5 to less than 25).

Healthy weight range for a height

Rearranging the formula gives the weight at any BMI:

Weight (lb) = BMI × height (in)² ÷ 703

At 68 inches:

  • BMI 18.5: 18.5 × 4,624 ÷ 703 = 121.7 lb
  • BMI 25: 25 × 4,624 ÷ 703 = 164.4 lb

So the healthy BMI range at 5 ft 8 in runs from about 122 lb up to just under 164 lb.

CDC BMI Categories for Adults

BMI Category
Less than 18.5 Underweight
18.5 to less than 25 Healthy weight
25 to less than 30 Overweight
30 to less than 35 Obesity, class 1
35 to less than 40 Obesity, class 2
40 or greater Obesity, class 3 (severe)

These categories apply to adults aged 20 and older.

What BMI Doesn’t Tell You

It can’t tell muscle from fat

Two people with the same height and weight have the same BMI, even if one carries much more muscle. Very muscular people can land in the overweight range without carrying excess fat. A body fat calculator looks at body composition rather than weight alone.

It doesn’t show where fat is carried

BMI says nothing about fat distribution. Waist measurements and other assessments give different information, which is one reason the CDC describes BMI as a screening measure to be considered with other factors.

It’s not for children

For anyone under 20, BMI is compared against growth charts for age and sex. The adult categories above don’t apply.

Tips for Using the Calculator

Measure height without shoes

Small errors in height have a big effect because height is squared. An inch too tall lowers the result noticeably. Stand straight against a wall, without shoes, and measure to the top of the head.

Weigh at a consistent time

Body weight changes through the day. If you’re tracking BMI over time, weigh at the same time of day, on the same scale, in similar clothing.

Use it as one number among several

BMI is most useful as a quick check and for following changes over time. For questions about your own health, weight or what a result means for you, a doctor can look at BMI alongside other measures. To see the calories a body needs at its current weight, try the calorie calculator.

Frequently Asked Questions

How is BMI calculated?

BMI is weight in kilograms divided by height in meters squared. In US units it is 703 times weight in pounds, divided by height in inches squared. For someone 5 ft 8 in (68 inches) and 160 lb, that's 703 × 160 ÷ 4,624, which is a BMI of 24.3.

What is a healthy BMI for adults?

The CDC classes a BMI from 18.5 to less than 25 as a healthy weight for adults 20 and older. Under 18.5 is underweight, 25 to less than 30 is overweight, and 30 or more is obesity.

What are the obesity classes?

The CDC divides obesity into three classes. Class 1 is a BMI of 30 to less than 35, class 2 is 35 to less than 40, and class 3, also called severe obesity, is a BMI of 40 or higher.

Is BMI accurate?

BMI is a screening measure, not a diagnosis. It doesn't measure body fat directly, so it can't tell muscle from fat or show where fat is carried. The CDC notes that it should be considered alongside other factors when assessing someone's health.

Does this BMI calculator work for children and teens?

No. These categories are for adults 20 and older. For children and teens, BMI is compared with growth charts for the same age and sex, giving a percentile rather than a fixed category, so it needs a different calculator.

What weight range is healthy for my height?

The calculator shows the weight range that gives a BMI from 18.5 to just under 25 at your height. At 5 ft 8 in, that is about 122 to 164 pounds. Our ideal weight calculator also compares several published ideal-weight formulas.

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