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BMI Calculator

BMI compares your weight to your height and places the result in one of the World Health Organization's categories. It is a rough screening figure used for populations, and it has real limitations for individuals — those are set out below rather than buried.

Units
BMI thresholds

Health authorities across South and East Asia use lower cut-offs, because risk rises at a lower BMI in those populations

Enter your weight and height to see your BMI.

BMI is a screening figure, not a diagnosis

BMI compares weight to height and knows nothing about body composition. It over-estimates body fat in muscular people and under-estimates it in older adults who have lost muscle. It is not valid for children, pregnant women, or people under about 1.5 m. Speak to a doctor before acting on it.

How to use this tool

  1. Choose metric (kilograms and centimetres) or imperial (pounds, feet and inches).
  2. Enter your weight.
  3. Enter your height. In imperial mode, use both the feet and inches fields.
  4. Your BMI, its category, and the healthy weight range for your height appear underneath.

Formula and method

Metric

BMI = weight (kg) ÷ height (m)²

Height is squared, which is why BMI treats a tall person's extra weight differently from a short person's.

Imperial

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

The 703 factor converts pounds and inches into the metric result. This calculator converts your input to kilograms and metres and uses the metric formula, so both unit systems give identical answers.

Worked examples

70 kg at 175 cm

  1. Convert height to metres: 175 ÷ 100 = 1.75
  2. Square it: 1.75 × 1.75 = 3.0625
  3. Divide: 70 ÷ 3.0625 = 22.9

A BMI of 22.9, which is in the healthy range.

180 lb at 5 ft 10 in

  1. Convert height to inches: (5 × 12) + 10 = 70
  2. Square it: 70 × 70 = 4900
  3. Apply the formula: 703 × 180 ÷ 4900 = 25.8

A BMI of 25.8, just inside the overweight range.

Notes and limitations

  • BMI is a screening tool, not a diagnosis, and it says nothing about body composition. Muscle is denser than fat, so athletes routinely score as overweight while carrying very little fat.
  • It under-estimates body fat in older adults who have lost muscle mass, and it does not account for where fat is carried, which matters more for health risk than the total.
  • The WHO thresholds used here are for adults. Children and teenagers are assessed against age- and sex-specific percentile charts instead, and this calculator should not be used for them.
  • The thresholds were derived largely from European populations. Several health bodies use lower cut-offs for people of South Asian, Chinese and other Asian descent, where health risks appear at a lower BMI.
  • BMI is not appropriate during pregnancy, and it is unreliable for people who are very short or very tall.
  • This tool does not give medical advice. Discuss any concern about your weight with a doctor, who can consider factors BMI ignores.

Frequently asked questions

What is a healthy BMI?

The World Health Organization treats 18.5 to 24.9 as the healthy range for adults, with below 18.5 underweight, 25 to 29.9 overweight, and 30 or above obese. These are population thresholds, not personal targets.

How do I calculate BMI by hand?

In metric, divide your weight in kilograms by your height in metres squared. In imperial, divide your weight in pounds by your height in inches squared and multiply by 703.

Is BMI accurate for muscular people?

No. BMI cannot tell muscle from fat, so a well-trained athlete can easily register as overweight or obese while having low body fat. Body fat percentage or a waist measurement is more informative for them.

Can I use this for my child?

No. Children's BMI is interpreted against growth charts for their age and sex, because healthy body composition changes as they grow. Ask a paediatrician or use a dedicated child BMI chart.

Why do some countries use different BMI thresholds?

Because the risk associated with a given BMI varies between populations. Health authorities in several Asian countries use a lower overweight threshold, as cardiovascular and diabetes risk tends to appear at a lower BMI than the standard cut-offs suggest.

What is the healthy weight range for my height?

It is the weight that puts your BMI between 18.5 and 24.9. The calculator works this out for the height you entered and shows it in whichever units you selected.

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