BMI Calculator for Adults (With Body Fat Check for Lifters)

What BMI tells you

Body mass index compares your weight with your height: BMI = weight (kg) ÷ height (m)². It was devised by the Belgian statistician Adolphe Quetelet in the 1830s and named "body mass index" by Ancel Keys in 1972. Doctors and researchers still use it because it's quick and works well across large groups of people: on average, higher BMIs go with higher health risks.

BMI categories for adults

Under 18.5: underweight
18.5–24.9: healthy weight
25–29.9: overweight
30–34.9: obese (class 1)
35–39.9: obese (class 2)
40 and above: obese (class 3)

A WHO expert consultation found that health risks rise at lower BMIs in many Asian populations and suggested cut-offs of 23 for overweight and 27.5 for obesity. Tick "Use Asian BMI cut-offs" to apply them.

What BMI misses

BMI can't tell muscle from fat, and it doesn't know where you carry your weight. That leads to two common mistakes:

Muscular people look "overweight". A 5'10" lifter at 195 lb and 12% body fat has a BMI of 28.
"Normal" BMI can hide high body fat, especially in people with little muscle. This is sometimes called being skinny-fat.

That's why this calculator asks for your body fat percentage (optional). With it, you'll see your lean mass, fat mass and FFMI, and whether your BMI and body fat agree. Don't know your body fat? The body fat calculator estimates it with a tape measure.

Other numbers on this page

Healthy weight range: every weight that gives a BMI of 18.5–24.9 at your height, and how far you are from it.
BMI Prime: your BMI divided by 25, the top of the healthy range. 1.0 is right at the limit.
New BMI: Oxford mathematician Nick Trefethen proposed 1.3 × weight ÷ height^2.5 in 2013, arguing that dividing by height squared makes tall people look heavier and short people lighter than they are. At 1.69 m (5'6.5") both formulas agree.

Where to go from here

BMI is a starting point, not a goal. To pick a realistic goal weight, try the Ideal Weight Calculator for Lifters, which includes Dr. Steven Halls' People's Choice formula and a muscle-aware ideal weight. To get there, the calorie calculator sets your daily target. And if you're lifting while you lose weight, log your sessions in GymGod or a notebook: rising lifts with a falling scale means you're losing fat, not muscle.

Sources

World Health Organization. A healthy lifestyle: WHO recommendations (BMI classification for adults).
WHO Expert Consultation. Appropriate body-mass index for Asian populations and its implications for policy and intervention strategies. Lancet. 2004;363(9403):157–163.
Keys A, Fidanza F, Karvonen MJ, Kimura N, Taylor HL. Indices of relative weight and obesity. J Chronic Dis. 1972;25(6):329–343.
Trefethen LN. New BMI (new body mass index). University of Oxford, Mathematical Institute; 2013.

Frequently asked questions

How is BMI calculated?

BMI is your weight in kilograms divided by your height in meters squared. In pounds and inches, it's 703 × weight ÷ height². For example, 180 lb at 5'10" (70 inches) is 703 × 180 ÷ 4,900 = 25.8.

What is a healthy BMI?

For adults, the World Health Organization classes 18.5–24.9 as healthy weight, 25–29.9 as overweight and 30 or above as obese. A WHO expert consultation suggested lower cut-offs for Asian populations, because health risks start at lower BMIs: overweight from 23 and obese from 27.5.

Is BMI accurate for athletes and people who lift?

Not on its own. BMI only uses height and weight, so muscle counts the same as fat. Many lifters are "overweight" by BMI at a low body fat percentage. Add your body fat percentage to this calculator to see which one your extra weight is.

Can I use this BMI calculator for children?

No. Children's BMI has to be compared with growth charts for their age and sex, so adult categories don't apply. Use a pediatric BMI calculator or ask your child's doctor.

What is BMI Prime?

BMI Prime is your BMI divided by 25, the top of the healthy range. A BMI Prime of 1.0 is right at the limit, 1.1 is 10% over it, and 0.9 is 10% under it. It makes it easy to see how far you are from the upper limit.

BMI Calculator