Calculator
BMI Calculator
Body Mass Index from height and weight, with a standard category.
What is BMI?
Body Mass Index (BMI) is a quick screening number that compares your weight to your height. It doesn’t measure body fat directly, but it’s a fast, free way to flag whether your weight falls in a typical range for your height — and it’s the same method doctors’ offices use as a first pass before anything more detailed.
Frequently asked questions
How is BMI calculated?
BMI = weight (kg) ÷ height (m)². If you're working with pounds and inches, the equivalent formula is weight (lb) ÷ height (in)² × 703 — this calculator converts for you under the hood when you switch to US units, so you get the same BMI value either way. It's a quick ratio, not a body-composition measurement.
What is a normal BMI range?
For adults, 18.5 to 24.9 is classified as a normal weight range. Below 18.5 is considered underweight, 25 to 29.9 is overweight, and 30 or above is classified as obese. These thresholds are population-level guidelines, not individual diagnoses.
Is BMI accurate for everyone?
No. BMI doesn't distinguish muscle from fat, so it can overestimate body fat in very muscular people and underestimate it in older adults who've lost muscle mass. It also doesn't account for where fat is distributed on the body, which matters for health risk. It's a fast screening tool, not a diagnosis.
How is BMI different from body fat percentage?
BMI only uses height and weight, so it can't tell muscle from fat. Body fat percentage estimates how much of your weight is actually fat tissue, using measurements like skinfold thickness or circumference. For a more direct estimate, use our Body Fat Calculator alongside this one.
BMI is a screening tool, not a diagnosis. It doesn’t account for muscle mass, bone density or body composition — talk to a healthcare provider for a full picture.