calcanswers.com All calculators

BMI Calculator for Adults

Health

Enter your height in feet and inches and your weight in pounds, or switch to centimeters and kilograms. You get your BMI, the adult weight category it falls in and the weight range that counts as healthy for your height.

Units

0 to 11. Example: 5 ft 9 in is 5 feet and 9 inches.

Use a period for decimals, like 12.5. Commas for thousands are fine. The result updates as you type.Decimals with a period, like 12.5

Your entries stay on your device. The math runs right in your browser.

Result: Your BMI

23.6kg/m²

Your BMI is 23.6 kg/m². The adult category for that is: Healthy weight.

  • Category (adults): Healthy weight
  • Healthy weight for your height from: 125.3 lb
  • Healthy weight for your height up to: 168.6 lb

Step by step

BMI = 23.6 kg/m²

  1. Your height in inches: 69 in.
  2. Weight in kilograms divided by height in meters squared gives 23.6 kg/m².
  3. Category for adults: Healthy weight.

Formula

BMI = weight (kg) / height (m)2
BMI = 703 × weight (lb) / height (in)2
weight
body weight in kilograms or pounds
height
height in meters, or in inches (feet × 12 + inches)
703
the CDC factor for pounds and inches (about 703; the unrounded value is 703.0696)

How it works

Body mass index compares your weight with your height: weight in kilograms divided by height in meters squared. With US units the calculator converts exactly, 1 pound = 0.45359237 kg and 1 inch = 2.54 cm. That is the same as the shortcut the CDC gives, BMI = 703 × pounds / inches², up to a rounding difference in the second decimal. Someone 5 ft 9 in (69 inches) tall weighing 160 lb has a BMI of 703 × 160 / 69² = 23.6.

The adult BMI chart of the CDC and the National Institutes of Health is the same for men and women 20 and older: under 18.5 underweight, 18.5 to 24.9 healthy weight, 25 to 29.9 overweight and 30 or more obesity, which is split into class 1 (30 to 34.9), class 2 (35 to 39.9) and class 3 (40 or more, severe obesity). The calculator rounds your BMI to one decimal first, so 24.97 shows as 25.0 and counts as overweight. The healthy weight range runs from 18.5 times your height in meters squared to 24.9 times it, converted to pounds, the same band the CDC and NIH calculators use (125.3 to 168.6 lb at 5 ft 9 in).

BMI is a screening number, not a diagnosis. It does not tell fat from muscle, so very muscular people can read as overweight, and older adults who have lost muscle can read too low. Waist size, blood pressure, blood sugar and cholesterol say more about health risk. Children and teens need BMI-for-age percentiles instead of these adult cutoffs, so this calculator is for adults only. To convert your weight between pounds and kilograms, use the kg to lbs converter.

The formula

Convert your height to inches first: 5 ft 4 in is 5 × 12 + 4 = 64 inches. Then square it (64 × 64 = 4,096), divide your weight by that number and multiply by 703. At 145 lb: 145 / 4,096 × 703 = 24.9.

The factor comes from 0.45359237 / 0.0254², about 703.0696, which the CDC rounds to 703. The calculator uses the exact unit conversion, which is why its result can differ from a hand calculation with 703 in the second decimal place.

Example

You are 5 ft 9 in and weigh 160 pounds. What is your BMI?

  1. Height in inches: 5 × 12 + 9 = 69 in. Squared: 69 × 69 = 4,761.
  2. BMI: 703 × 160 / 4,761 = 23.6 kg/m², a Healthy weight result.
  3. At this height the healthy range runs from 125.3 lb to 168.6 lb.

Your BMI is 23.6 kg/m². The adult category for that is: Healthy weight.

Load this example into the calculator

Frequently asked questions

Is BMI different for women and men?

No, not for adults. The formula and the categories are the same for women and men aged 20 and older. Women tend to have more body fat than men at the same BMI, which is one of the reasons BMI is only a screening tool. For children and teens, BMI is compared with others of the same age and sex.

What is a healthy BMI for adults?

A BMI from 18.5 to 24.9 is the healthy weight range for adults. Below 18.5 is underweight, 25 to 29.9 is overweight and 30 or higher is obesity. Your doctor may look at other measures as well, such as waist circumference.

How do I calculate BMI by hand?

Multiply your weight in pounds by 703, then divide by your height in inches squared. For 180 lb at 5 ft 11 in (71 inches): 180 × 703 = 126,540; 71 × 71 = 5,041; 126,540 / 5,041 = 25.1. In metric, divide kilograms by meters squared.

Is BMI accurate for athletes and older adults?

It can mislead in both. Muscle weighs more than fat, so athletes can have a BMI in the overweight range while being lean. Older adults often lose muscle, so their BMI can look healthy even with extra body fat. Talk to a health care provider if your result surprises you.

Does age change my BMI category?

Not for adults. The CDC and NIH use the same cutoffs for everyone aged 20 and older, so a BMI of 27 counts as overweight at 25 and at 65. Age changes what the number means rather than the category: older adults with a healthy BMI may have less muscle than younger people, and for people 65 and older a slightly higher BMI may help protect against thinning bones. A result near a cutoff is worth discussing with your provider. Only children and teens get age-specific BMI-for-age percentiles.

Can I use this calculator for my child?

No. For ages 2 to 19, BMI is plotted on the CDC growth charts as a percentile for age and sex. The adult cutoffs such as 25 and 30 do not apply to children and teens.

Last updated: Responsible editor: Jared Alan
Checked against 13 test cases · How we test
Sources: