Body Mass Index is a quick screening tool — it doesn't account for muscle mass, bone density, or body composition.
Below 18.5 — Underweight · 18.5–24.9 — Normal weight · 25–29.9 — Overweight · 30 and above — Obese.
BMI is a general screening measure, not a diagnosis. Talk to a healthcare provider for a full picture of your health.
Body Mass Index compares your weight to your height using a simple ratio. In metric units, it's your weight in kilograms divided by your height in meters, squared:
BMI = weight (kg) / height (m)²
In imperial units, the calculator uses the equivalent formula: weight in pounds × 703, divided by height in inches squared. Both formulas give the same result — they're just different unit conventions for the same measurement.
Someone who is 170 cm tall and weighs 70 kg has a BMI of 70 ÷ (1.70 × 1.70) = 24.2, which falls in the "Normal weight" range (18.5–24.9).
In imperial units, someone at 5 ft 7 in (67 inches) and 154 lb gets the same result: (703 × 154) ÷ (67 × 67) = 24.1.
Is BMI accurate for everyone?
No. BMI doesn't distinguish between muscle and fat, so athletes and very muscular people are often classified as "overweight" despite having low body fat. It also doesn't account for age, sex, or where fat is distributed on the body.
What's a healthier alternative to BMI?
Waist circumference, waist-to-hip ratio, and body fat percentage all give a more complete picture. Our Body Fat Calculator is a useful next step.
Does BMI apply the same way to children?
No — children and teens are assessed using age- and sex-specific BMI percentiles, not the fixed adult categories used here. This calculator is intended for adults.
My BMI says "overweight" but I feel healthy — should I worry?
BMI is a screening tool, not a diagnosis. If you have concerns about your weight or health, the most reliable next step is a conversation with a doctor who can look at your full picture.
BMI = weight (kg) divided by height (m) squared. If using pounds and inches, the formula is BMI = 703 x weight (lb) divided by height (in) squared.
Standard adult ranges are: below 18.5 underweight, 18.5-24.9 normal, 25-29.9 overweight, and 30+ obese, though these cutoffs are general guidelines, not diagnoses.
No — BMI doesn't distinguish between muscle and fat, so very muscular people can show a "high" BMI despite low body fat. It's a screening tool, not a precise health measure.