BMI Calculator
Calculate your Body Mass Index (BMI) from height and weight and see your weight category
Last updated: 2026-07-10
Body Mass Index (BMI) is a simple screening measurement that estimates whether your weight is healthy for your height. It's calculated by dividing your weight in kilograms by the square of your height in meters. Doctors, insurers, and fitness professionals use BMI as a quick, low-cost way to flag potential weight-related health risks -- it doesn't require any special equipment beyond a scale and a tape measure. Our free BMI calculator instantly computes your BMI and tells you which standard weight category you fall into, so you can get a quick read on where you stand.
How BMI Is Calculated
weight in kilograms divided by height in meters, squared
**Example:** A person weighing 70 kg who is 170 cm (1.70 m) tall: BMI = 70 / (1.70 × 1.70) BMI = 70 / 2.89 BMI = 24.2 (Normal weight) **Standard BMI categories (adults):** - Below 18.5: Underweight - 18.5 – 24.9: Normal weight - 25.0 – 29.9: Overweight - 30.0 and above: Obese This calculator accepts weight in kilograms and height in centimeters (converted to meters internally) since that's the most common metric input pairing.
Use Cases
General Health Screening
Get a quick estimate of whether your weight falls in a healthy range for your height, as a starting point for a conversation with your doctor.
Fitness and Weight-Loss Tracking
Track how your BMI changes over time alongside a diet or exercise program, as one of several signals (along with body composition) of progress.
Insurance and Wellness Programs
Many employer wellness programs and life insurance applications use BMI as a quick risk-screening metric.
Pre-Appointment Preparation
Calculate your BMI before a medical checkup so you can discuss your weight category and any related risk factors with your healthcare provider.
Frequently Asked Questions
What is a healthy BMI?
For most adults, a BMI between 18.5 and 24.9 is considered a healthy ("normal") weight range. Below 18.5 is classified as underweight, 25.0-29.9 as overweight, and 30.0 or above as obese.
Is BMI accurate for everyone?
BMI is a useful screening tool but it doesn't distinguish between muscle and fat mass, so it can overestimate body fat in muscular athletes and underestimate it in older adults who have lost muscle mass. It also isn't validated for children (who need age- and sex-specific percentile charts) or during pregnancy. Use it as one data point, not a diagnosis.
What units does this calculator use?
This calculator takes weight in kilograms (kg) and height in centimeters (cm). If you have measurements in pounds or feet/inches, convert them to kilograms and centimeters first (1 lb ≈ 0.4536 kg, 1 inch = 2.54 cm).
Why does BMI use height squared?
Body weight tends to scale roughly with the square of height across a population, so dividing by height squared (rather than height itself) produces a metric that's less biased by how tall or short someone is. It's an empirical approximation, not an exact biological law, which is part of why BMI has known limitations.
What should I do if my BMI is outside the normal range?
A BMI outside 18.5-24.9 doesn't automatically mean a health problem, but it's worth discussing with a doctor, especially alongside other factors like waist circumference, body composition, diet, and activity level. A healthcare provider can give you a fuller picture than BMI alone.
Ad Space (AdSense)