BMI Calculator

Check your body mass index in seconds with this free BMI calculator for adults. Pick US or metric units, type your weight and height, and see your BMI plus the weight category it falls in. Adults use it for a quick health snapshot. Everything runs in your browser, so your numbers never leave your device.

How BMI is worked out

Metric: BMI = weight in kilograms divided by (height in meters times height in meters). US: BMI = (weight in pounds divided by (height in inches times height in inches)) times 703. The answer puts you in one of four groups: Underweight below 18.5, Normal from 18.5 to 24.9, Overweight from 25 to 29.9, and Obese at 30 and above.

Solved example: 70 kg and 175 cm

An adult weighs 70 kilograms and stands 175 centimeters tall. Here is the math, step by step. Step 1: turn 175 cm into meters: 1.75 m. Step 2: square the height: 1.75 times 1.75 = 3.0625. Step 3: divide the weight: 70 divided by 3.0625 = 22.9. The BMI is 22.9, which falls in the Normal group (18.5 to 24.9).

How to use this calculator

  1. Pick the unit system you like: US (lb, in) or Metric (kg, cm).
  2. Type your weight and height into the two boxes.
  3. Press Calculate and read your BMI and its weight category.

Limits: BMI is not medical advice

BMI is a rough screening number, not a diagnosis and not medical advice. It does not measure body fat, muscle, or bone density, so very muscular adults can land in the Overweight group without extra fat. It is less useful for pregnant women, older adults, and children, and it does not look at where fat sits on the body. Talk to a doctor before you act on your result.

Frequently asked questions

Who should not rely on a BMI calculator for adults?

Adults with a lot of muscle, pregnant women, and people over 65 get the least useful results. Muscle weighs more than fat, so athletes often score higher than their body fat suggests. In these cases a tape measure around the waist or a doctor’s check gives a better picture.

Why does muscle change what BMI means?

BMI only looks at weight and height. It cannot tell the difference between heavy muscle and extra fat. A strong person can have a BMI of 26 and be perfectly healthy, while a person with a BMI of 22 but little muscle can still carry risky belly fat.

How often should I check my BMI?

For most adults, once a month is plenty. Weight moves up and down day to day, so one reading means little. Weigh yourself on the same day each month, at the same time, and watch the trend over three to six months.

Why does the tool ask for inches instead of feet and inches?

The US formula works with total inches, so one number keeps the math simple. If you are 5 feet 8 inches tall, that is (5 times 12) + 8 = 68 inches. Type 68 into the height box.

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