CalcDuck

BMI Calculator

BMI Calculator

Units
cm
kg
Your BMI
22.9
Category
Normal weight
Healthy weight range for your height
56.7–76.3 kg

BMI (body mass index) is your weight in kilograms divided by your height in meters squared. Someone weighing 70 kg at 175 cm has a BMI of 70 ÷ 1.75² = 22.9. The WHO classifies adult BMI under 18.5 as underweight, 18.5–24.9 as normal weight, 25–29.9 as overweight, and 30 or above as obese. BMI is a screening measure, not a diagnosis, and does not distinguish muscle from fat.

Tip: “Copy with settings” shares a link that opens this calculator with your numbers already filled in.

How this calculator works

Enter your height and weight in either metric or imperial units and the calculator returns your BMI, your WHO category, and the weight range that would put you in the normal band for your height.

BMI is a screening measure, not a diagnosis. It says nothing about how your weight is distributed between muscle and fat, which is why very muscular people often land in "overweight" while being metabolically healthy. Treat the number as a starting point for a conversation, not a verdict.

The formula

BMI = weight (kg) ÷ height (m)²Imperial inputs are converted exactly first: 1 lb = 0.45359237 kg, 1 in = 2.54 cm

Worked example: 160 lb at 5'9"

  1. Convert: 160 lb × 0.45359237 = 72.57 kg; 69 in × 2.54 = 175.26 cm = 1.7526 m.
  2. BMI = 72.57 ÷ 1.7526² = 72.57 ÷ 3.0716 = 23.6.
  3. 23.6 falls in the 18.5–24.9 band: normal weight.

Frequently asked questions

Is BMI accurate for athletes?

Often not. Muscle is denser than fat, so strength athletes routinely show BMI 25–30 with low body fat. Waist circumference or a body-fat measurement gives a better picture in that case.

Do the same cutoffs apply to children?

No. For ages 2–19, BMI is compared against age- and sex-specific growth percentiles rather than fixed cutoffs. This calculator uses the adult thresholds.

What are the exact WHO categories?

Underweight below 18.5, normal weight 18.5–24.9, overweight 25–29.9, and obesity 30 and above, subdivided into class I (30–34.9), II (35–39.9) and III (40+).

Why does the calculator show a healthy weight range?

It inverts the formula: the range is 18.5 × height² to 24.9 × height², the weights that would place your BMI inside the normal band.

Can two people have the same BMI but very different amounts of body fat?

Yes. BMI only uses weight and height, so it cannot distinguish muscle from fat. Two people of identical height and weight can have quite different amounts of muscle versus fat — and therefore different builds — even though their BMI number is identical. This is the same reason muscular athletes often land in the 25-30 'overweight' band despite low body fat.

Sources

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