BMI Calculator

For most US adults age 20 and older, a healthy BMI falls between 18.5 and 24.9. A 5-foot-6 woman weighing 130 lbs scores 21.0, right in the middle of that range. A 6-foot man at 175 lbs scores 23.7 and also lands in the healthy zone. Below 18.5 is underweight, 25.0 to 29.9 is overweight, and 30.0 and above is obese. These cutoffs come from the CDC and World Health Organization and apply to both men and women. They do not apply to children under 20, who use age-and-sex-specific percentile charts instead, or to pregnant women, whose BMI targets differ by trimester. If your number lands at 24.8 or 25.1, treat it as a borderline reading rather than a hard line. A half-inch measurement error can move you across the threshold. To see how your weight translates into daily calorie needs at that BMI, run the tdee-calculator next.

The 703 constant converts imperial units into the metric scale the original BMI formula uses. The metric formula is weight in kilograms divided by height in meters squared. Since one pound equals 0.453592 kilograms and one inch equals 0.0254 meters, squaring the height conversion and dividing gives 703.07, which is rounded to 703. A 5-foot-9 person at 160 lbs is 69 inches and 160 lbs, so 160 divided by 69 squared (4,761) equals 0.0336, and 0.0336 times 703 equals 23.6. That lands in the normal weight range. If you forget the 703, you get 0.0336, which looks meaningless. Some calculators skip the constant by converting to metric first, but the result is identical. The number itself is not arbitrary, it is just a unit conversion baked into the equation so you can enter pounds and inches directly.

Yes, BMI overestimates body fat in muscular people because muscle weighs more than fat per unit of volume. A 6-foot-2 linebacker weighing 240 lbs scores 30.8, which is classified as obese, even if his body fat is 12%. An NBA point guard at 6-foot-3 and 200 lbs scores 25.0, labeled overweight, despite being lean. The reverse also happens: an older adult who has lost muscle mass can score 24.5 at 5-foot-8 and 160 lbs while carrying a high body fat percentage, a condition called normal weight obesity. For these cases, body fat percentage or waist circumference gives a truer picture. A waist over 40 inches in men or 35 inches in women indicates visceral fat risk regardless of BMI. If you lift weights regularly, pair your BMI with a body fat measurement before drawing conclusions.

The answer depends on your current height and BMI, and you can back into it with the formula. Suppose you are 5-foot-6 (66 inches) and weigh 175 lbs. Your BMI is 175 divided by 4,356, times 703, which equals 28.2, in the overweight range. To hit a BMI of 24.9, you need a weight of 24.9 times 4,356 divided by 703, which is 154 lbs. That means losing 21 lbs, or about 12% of your body weight. A 5-foot-10 man at 210 lbs (BMI 30.1) needs to reach 173 lbs for a BMI of 24.8, a 37 lb drop. Losing 1 to 2 lbs per week is the standard pace, so the first example takes roughly 11 to 21 weeks. Even a 5% loss, about 9 lbs in the first case, improves blood pressure and blood sugar before you reach a normal BMI. Use the calorie-calculator to find a daily deficit that fits that timeline.

No, the BMI formula is identical for adult men and women. A 5-foot-4 woman at 140 lbs and a 5-foot-4 man at 140 lbs both score 24.0. What differs is how the same number is interpreted. Women naturally carry more essential fat, roughly 10% to 13% versus 2% to 5% for men, so a woman at BMI 24 may have a higher body fat percentage than a man at the same BMI. Women also tend to store fat in the hips and thighs, while men store more in the abdomen, which is metabolically riskier. Waist thresholds reflect this: 35 inches for women and 40 inches for men. Age matters too. Adults over 65 may have a slightly higher healthy BMI range, around 23 to 28, because some extra reserve protects against illness. For children and teens, BMI is plotted on growth percentiles by age and sex, not fixed cutoffs.

Use the number as a starting point, not a verdict. If your BMI is between 18.5 and 24.9, maintain it with 150 minutes of moderate activity per week, which is the CDC minimum for adults. If you are in the overweight range at 27.5, aim to lose 5% to 10% of your weight: at 180 lbs that is 9 to 18 lbs, which typically lowers blood pressure by several points. If your BMI is 30 or higher, ask your doctor about a structured program, since medical weight management is often covered at that threshold. In every case, measure your waist and note your activity level, because a 5-foot-9 person at 170 lbs with a 34-inch waist is in better shape than the BMI alone suggests. Next, calculate how many calories you burn daily with the tdee-calculator, then subtract 500 calories for a 1 lb per week loss. Pair that with the bmr-calculator to see your resting burn and set a floor for how low you should eat.