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BMI Calculator

Calculate Body Mass Index from height and weight, and see your World Health Organization weight category.

By The Calcumatix Team Reviewed by Calcumatix Editorial Review

Units

Result

22.9

Normal weight

BMI is a general screening tool, not a diagnosis. Consult a healthcare professional for personal advice.

Quick Answer

BMI is your weight in kilograms divided by your height in metres squared, so 70 kg at 1.75 m is 70 / 3.0625, which is a BMI of 22.9 in the normal range. In imperial units, BMI is 703 times weight in pounds divided by height in inches squared. This calculator shows the number and your WHO category.

What A BMI Calculator Does And How It Works

The BMI Calculator is a free health tool that estimates Body Mass Index, a screening figure that relates your weight to your height. Enter your height and weight in metric or imperial units, and the tool returns your BMI along with the World Health Organization weight category. In metric units, BMI is your weight in kilograms divided by your height in metres squared. For 70 kg at 1.75 m, that is 70 divided by 3.0625, which gives a BMI of 22.9 in the normal range. BMI sorts adults into four bands: underweight, normal weight, overweight, and obesity. It is a quick population-level screen, not a diagnosis, because it does not measure body fat directly or account for muscle, bone, or where fat sits. Use the number as a starting point and speak to a healthcare professional about what it means for you.

The BMI Calculator Formula And How It Is Applied

BMI uses one ratio of weight to height, with a conversion factor for imperial units.

  • Metric: BMI = weight (kg) / height (m) squared.
  • Imperial: BMI = 703 x weight (lb) / height (in) squared.

The World Health Organization sorts adults into four bands: below 18.5 is underweight, 18.5 to 24.9 is normal weight, 25 to 29.9 is overweight, and 30 or above is obesity.

The 703 factor in the imperial formula converts pounds and inches so the result matches the metric scale.

How To Use A BMI Calculator In Clear Steps

Inputs

  • Units: choose metric for kilograms and centimetres, or imperial for pounds, feet, and inches.
  • Weight: enter a current body weight in the selected unit.
  • Height: enter adult height in centimetres, or feet and inches.

Steps

  1. Select metric or imperial units.
  2. Enter your weight and height.
  3. Read your BMI and its weight category.
  4. Check the WHO scale on the right to see where you land.

BMI Calculator Example, Worked In Full

What is the BMI for 70 kg and 175 cm?

  1. Convert height to metres: 175 cm = 1.75 m.
  2. Square the height: 1.75 x 1.75 = 3.0625.
  3. Divide weight by that value: 70 / 3.0625 = 22.9.
  4. Rounding: BMI is shown to one decimal place, so 22.86 rounds to 22.9.

A BMI of 22.9 sits within the normal weight range.

When A BMI Calculator Gives The Right Answer

BMI is useful when you need a quick adult weight-to-height screening number. It can place the result beside standard WHO categories, which makes the number easier to read than weight alone.

The result is less useful for personal diagnosis. It does not measure body fat, muscle mass, bone density, waist size, or individual risk. Athletes, older adults, pregnant people, and children may need a different assessment.

For nearby tools, the health calculators hub links BMI with BMR and TDEE. The methodology page explains formula review, and the glossary defines BMI and related terms.

Assumptions

  • BMI applies to adults aged 20 and over; it is read differently for children and teens.
  • The World Health Organization cut-off points define the categories.
  • Height and weight are entered as accurate, current measurements.

The category shown is based only on the BMI number. It should be read as screening context, not as a personal health conclusion.

Limitations

  • BMI does not distinguish muscle from fat, so it can misclassify very muscular or older people.
  • It does not show where fat sits, which also affects health risk.
  • It is a screening tool only and does not diagnose any health condition.

In Practice

The most common mistake is treating BMI as a body-fat or health verdict. It is a screening ratio only: it cannot tell muscle from fat, so athletes can read as overweight and older adults as normal while carrying excess fat. Use BMI as a starting flag, then confirm with a professional rather than acting on the number alone.

Related Calculators

BMR Calculator

Estimate basal metabolic rate from age, sex, height, and weight, with metric or imperial inputs and a visible Mifflin-St Jeor example.

Open the Calculator

TDEE Calculator

Estimate total daily energy expenditure from BMR and activity level, with metric or imperial inputs, formula steps, and a worked example.

Open the Calculator

Frequently Asked Questions About BMI And Body Weight

What is a healthy BMI range for adults?

For most adults, the World Health Organization classifies a BMI between 18.5 and 24.9 as the normal range. This is general screening guidance for populations, not a personal diagnosis.

Is BMI accurate for athletes and muscular people?

BMI is often misleading for very muscular people. Because muscle is denser than fat, an athlete can have a high BMI without excess body fat, so BMI is a screening figure, not a body-composition measure.

How do I calculate BMI in imperial units?

Multiply your weight in pounds by 703, then divide by your height in inches squared. For 154 lb and 69 in, that is 703 x 154 / (69 x 69), which is about 22.7.

Does BMI apply to children the same way?

No, BMI is read differently for children and teens. For people under 20, BMI is compared with age and sex percentile charts rather than the fixed adult categories this tool uses.

Can BMI tell me my body fat percentage?

No. BMI uses only weight and height. It does not measure body fat percentage, muscle mass, bone density, or waist size.

Why can BMI be misleading for some adults?

BMI can be misleading when weight does not reflect body fat in a typical way. Very muscular adults, some older adults, pregnant people, and people with different body composition may need a professional assessment.

Sources

Reviewed for accuracy against the formula shown above.