BMI Calculator

When to use this calculator

BMI is the number most doctors' offices write down first, so it is a handy thing to know before a physical, an insurance screening, or a new fitness plan. Use this calculator if you want a quick baseline, you are tracking weight loss, or a wellness program has quoted a figure and you want to see where you land. It takes feet and inches with pounds, which is how most people in the US measure, but it will also take centimeters and kilograms if you prefer metric.

It is built for adults 18 and over. For most people it gives a reasonable first read on whether weight sits in a range linked to lower long-term risk — but it is a screening signal, not a diagnosis. A surprising number is a reason to look at your waist measurement, your activity, and your most recent labs, and to bring it up with your physician rather than to draw conclusions from the figure by itself.

Reading your result

The CDC uses the WHO bands, so your score falls into one of four groups. Below 18.5 is underweight, which can point to under-nutrition or an underlying condition. From 18.5 to 24.9 is the healthy-weight range, associated in large studies with the lowest all-cause risk. From 25 to 29.9 is overweight, and 30 or higher is obesity, which the CDC divides into Class I, II, and III as risk climbs.

Treat the band as a flag rather than a final answer. A score of 26 does not mean you are sick, and a score of 23 is no guarantee of good health — it depends on your muscle mass, where you carry fat, your blood pressure, and your HbA1c. The bands describe risk across populations, so use yours to decide whether a closer look is worth your time.

A worked example

Take an adult who is 5 feet 9 inches tall and weighs 165 pounds. Converting height to 69 inches, the imperial formula is 165 times 703 divided by 69 squared, which is 115,995 divided by 4,761 — a BMI of about 24.4, just inside the healthy-weight range. If the same person reached 180 pounds, their BMI would rise to about 26.6, putting them in the overweight band on a gain of 15 pounds. Modest weight changes shift the number more than people expect, so the trend over months matters more than any single reading.

Mistakes to watch for

BMI is easy to calculate but easy to over-read. Keep these limitations in mind before you put much weight on the figure.

• Mistaking it for a body-fat measurement — BMI can't separate muscle from fat, so athletes and heavily muscled people routinely score 'overweight' while carrying little fat.
• Ignoring fat location — a waist over 40 inches for men or 35 inches for women signals risk even when BMI looks normal, because visceral fat drives cardiometabolic disease.
• Applying adult bands to kids — children and teens 2 to 19 are assessed on BMI-for-age percentiles plotted on CDC growth charts, not these thresholds.
• Overlooking ethnicity — for Asian Americans the ADA recommends diabetes screening from a BMI of 23, because risk rises at a lower threshold than the standard bands suggest.

US health guidance and thresholds

In the US the CDC frames BMI as a screening tool that works alongside other measures, not as a diagnosis. The American Diabetes Association recommends earlier diabetes screening at a BMI of 23 or above for Asian Americans, and lower waist cut-offs of about 35.4 inches for men and 31.5 inches for women, because cardiometabolic risk in that population rises at smaller numbers. If that applies to you, read your result against the lower thresholds rather than the standard ones.

Whatever your score, the practical next steps are the same — check your waist circumference, look honestly at activity and diet, and review your blood pressure, lipid panel, and HbA1c with a clinician. A high BMI is a prompt for further testing, not a conclusion; a primary care provider can interpret the number in the context of your full health history and recent labs.