BMI Calculator
Body Mass Index from your height and weight.
Input sheet
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Body Mass Index is the quickest population-level screen for whether your weight falls in a healthy range for your height. It's the number most doctors glance at first, even though it's a starting point rather than a verdict.
How it works
BMI = 703 × weight(lb) ÷ height(in)². Normal is 18.5–24.9.
BMI uses the imperial shortcut: 703 times weight in pounds divided by height in inches squared. The 703 factor is what converts pounds and inches into the metric kg/m² scale the categories are defined on.
The standard cutoffs are under 18.5 underweight, 18.5-24.9 normal, 25-29.9 overweight, and 30 or above obese. These bands describe statistical health risk across large groups, not any individual's body composition.
BMI = 703 × weight(lb) ÷ height(in)².
Worked examples
Someone 5'10" (70 in) weighing 175 lb. → BMI 25.1 — just into the overweight band.
703 × 175 ÷ (70 × 70) = 123,025 ÷ 4,900 ≈ 25.1.
Someone 5'6" (66 in) weighing 150 lb. → BMI 24.2 — within the normal range.
703 × 150 ÷ (66 × 66) = 105,450 ÷ 4,356 ≈ 24.2.
Tips & gotchas
- Pair BMI with a waist measurement — abdominal fat carries more health risk than the BMI number alone reveals.
- Muscular athletes routinely read overweight or obese on BMI despite low body fat; don't let the label alarm you if you train hard.
- Track the trend over months rather than fixating on a single reading, which moves with hydration and meal timing.
- If you're near a cutoff, a body-fat estimate gives a far more useful picture than BMI's two decimal places.
FAQ
Is BMI accurate?
It is a rough screen — it does not distinguish muscle from fat, so athletes read high.
Why does BMI flag muscular people as overweight?
BMI only knows height and weight — it can't tell dense muscle from fat. A lean, muscular athlete weighs more for their height and so reads high despite being very fit.
Is a 'normal' BMI a guarantee of health?
No. Someone can sit in the normal band with little muscle and excess abdominal fat. BMI screens risk across populations; it doesn't certify any one person's health.
Does BMI work the same for everyone?
The cutoffs are general adult averages. They fit children, the elderly, pregnant people, and some ethnic groups poorly, which is why clinicians treat BMI as one input among several.
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