BMI calculator

Enter your height and weight to get your body mass index (BMI), the adult category it falls in, and the weight range that matches a BMI of 18.5 to 24.9 at your height.

By the Calcist team · Checked against known answers · Updated October 27, 2026

Private: calculated on your device. Nothing you type is sent anywhere.

Next: BMI can't tell muscle from fat. Estimate body fat with a tape measure in the body fat calculator, or see the ideal weight formulas for your height.

How BMI is calculated

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

Calcist converts US units to metric with the exact factors (1 lb = 0.45359237 kg, 1 in = 2.54 cm), which matches the 703 shortcut to within rounding.

Worked example

A person who is 5 ft 10 in (70 in, or 1.778 m) and weighs 160 lb (72.57 kg):

BMI = 72.57 ÷ 1.778² = 72.57 ÷ 3.161 = 22.96 ≈ 23.0

That falls in the 18.5–24.9 range. At that height, BMIs of 18.5 and 24.9 match weights of about 128.9 lb and 173.5 lb.

Adult BMI categories

BMI	Category (CDC and WHO)
Below 18.5	Underweight
18.5 to 24.9	Healthy weight
25.0 to 29.9	Overweight
30.0 to 34.9	Obesity, class 1
35.0 to 39.9	Obesity, class 2
40.0 and above	Obesity, class 3 (severe)

Calcist rounds BMI to one decimal and places it in the category for that rounded value, so the number and the category always agree.

BMI Prime

BMI Prime is your BMI divided by 25, the top of the healthy range. A value of 1.00 sits right at that upper limit. 0.92 means 8% below it, and 1.20 means 20% above it. It was proposed by Gadzik (2006) as an easier way to compare against the upper limit.

When BMI doesn't tell the whole story

Muscle. BMI only uses height and weight. A muscular person can have a high BMI with little body fat. A body fat estimate can help.
Age. Older adults tend to have more body fat than younger adults at the same BMI.
Ethnicity. Health risks start at lower BMIs in some groups. A WHO expert panel noted this for Asian populations.
Pregnancy. BMI isn't used to judge weight during pregnancy. Ask your prenatal care provider.
Children and teens. The CDC reads BMI for ages 2 to 19 as a percentile for age and sex, not with the adult categories.

BMI is a screening number, not a diagnosis. A doctor looks at it alongside other measures, such as waist size, blood pressure and blood tests.

For anyone under 18, these calculators show a pointer to the CDC's BMI-for-age calculator and growth charts instead of adult results, because children and teens are still growing.

Sources

CDC: Adult BMI categories
WHO: Obesity and overweight fact sheet
CDC: BMI calculator for children and teens (ages 2–19)
WHO Expert Consultation. Appropriate body-mass index for Asian populations and its implications for policy and intervention strategies. Lancet 2004;363:157–163.
Gadzik J. "How much should I weigh?" Quetelet's equation, upper weight limits, and BMI prime. Connecticut Medicine 2006;70(2):81–88.

How we checked this

Before every update, this calculator is run in a real browser with these known answers, and it must match all of them:

5 ft 10 in, 160 lb: BMI 23.0, healthy weight ✓
Healthy range at 5 ft 10 in: 128.9–173.5 lb ✓
180 cm, 90 kg: BMI 27.8, overweight ✓
160 cm, 110 kg: BMI 43.0, class 3 obesity ✓
5 ft 10 in, 200 lb: 26.5 lb over the healthy range (short value, no wrap) ✓
165 cm, 45 kg: 5.4 kg under the healthy range ✓
5 ft 10 in, 160 lb: in range ✓
Age 15: points to CDC BMI-for-age charts instead ✓

Last checked October 26, 2026. Spotted something wrong? The math is done in your browser with the formula shown on this page, so you can check any result by hand.

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Questions people ask

What is a healthy BMI?

For adults, the CDC and WHO use 18.5 to 24.9 as the healthy weight range. It's a population guide, and a doctor may look at other measures for you.

Is BMI accurate for athletes?

Often not. Muscle is dense, so muscular people can have a BMI in the overweight range without much body fat.

How do I calculate BMI in pounds and inches?

Multiply your weight in pounds by 703, then divide by your height in inches squared. 160 lb at 70 in: 703 × 160 ÷ 4,900 = 22.96.

Why is BMI different for children?

Children's body fat changes as they grow, so the CDC compares a child's BMI with others of the same age and sex using percentiles.

What is BMI Prime?

Your BMI divided by 25. Below 1.00 means under the upper limit of the healthy range, and above 1.00 means over it.

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Body fat calculatorBody fat % from a tape measure (U.S. Navy method), with the ACE chart.Ideal weight calculatorRobinson, Miller, Devine and Hamwi formulas plus the BMI healthy range.Calorie calculatorDaily calories to maintain, lose or gain weight at a steady rate.TDEE calculatorTotal daily energy expenditure at every activity level.