BMI calculator

Body mass index is weight divided by the square of height. It is a screening measure for populations, and a blunt one for individuals — it cannot tell muscle from fat.

Weight

Height

BMI

22.86kg/m2

= Exact Healthy weight

BMI prime BMI divided by 25: below 1 is inside the healthy range.: 0.914
Bottom of the healthy range: 56.7
Top of the healthy range: 76.3
Distance above the healthy range Negative means you are inside or below it.: -6.3

Show the working

Weight = 70
Height = 175
h_m = 175 / 100 = 1.75
BMI = 70 / 1.75^2 = 22.8571
BMI prime = 22.8571 / 25 = 0.914 286
Bottom of the healthy range = 18.5 * 1.75^2 = 56.6563
Top of the healthy range = 24.9 * 1.75^2 = 76.2563
to_min = 70 - 56.6563 = 13.3438
Distance above the healthy range = 70 - 76.2563 = -6.256 25

Values are shown to six significant figures here; the arithmetic itself runs on exact fractions and is only rounded where a number is printed.

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The formula

BMI = weight in kilograms / (height in metres)^2
In imperial units: BMI = 703 x weight in pounds / (height in inches)^2
BMI prime = BMI / 25

The WHO cut-offs used here were derived from European populations. Several health bodies use lower thresholds for people of South Asian descent, where cardiometabolic risk rises at a lower BMI.

BMI treats a heavily muscled athlete and a sedentary person of the same weight identically, which is its central weakness.

This is a population formula, not a diagnosis. Individual metabolism, body composition and medical history all move the real answer, so treat the number as a starting point and talk to a clinician about anything that matters.

Frequently asked

What is a healthy BMI?

The WHO puts the healthy range at 18.5 to 24.9 kg/m2 for adults.

How do you calculate BMI in pounds and inches?

Multiply weight in pounds by 703, then divide by height in inches squared. This calculator does the conversion exactly if you switch the unit selectors.

Is BMI accurate?

It is a reasonable screening tool across a population and unreliable for any one person, especially athletes, the elderly, and anyone very tall or very short.