BMI Calculator
Calculate your Body Mass Index (BMI) in metric or imperial units.
Body Mass Index (BMI) is a quick screen that compares your weight to your height. This calculator works in both metric and imperial units, shows your BMI to one decimal place, and tells you which standard category it falls into.
BMI is a starting point, not a diagnosis. It doesn't know the difference between muscle and fat, and it reads differently across ages and body types. Use it as one signal among many.
How to use the BMI calculator
- Choose metric (cm / kg) or imperial (ft-in / lb).
- Enter your height and weight.
- Read your BMI and its category below.
BMI categories
For adults, the World Health Organization uses these ranges:
- Under 18.5 — underweight
- 18.5 to 24.9 — healthy weight
- 25 to 29.9 — overweight
- 30 and above — obese
The formula is weight in kilograms divided by height in metres squared. In imperial units it's weight in pounds times 703, divided by height in inches squared.
What BMI doesn't tell you
Because BMI only uses height and weight, a muscular athlete can score "overweight" while carrying very little fat, and an older person who has lost muscle can score "healthy" while carrying more. It also isn't designed for children, pregnant people, or specific clinical decisions. Treat it as a fast, free screening number and talk to a healthcare professional for anything that matters.
Using BMI sensibly over time
A single BMI reading is a snapshot; the trend is more informative. Tracking the number over months, alongside how your clothes fit and how you feel, tells you far more than one calculation ever could. Because BMI ignores where fat sits, many clinicians pair it with a waist measurement — carrying weight around the middle carries more health risk than the same weight on the hips and thighs. If your BMI sits near a category boundary, that context matters even more.
Metric and imperial, side by side
The two systems give the same result from the same body — only the units differ. In metric, a 1.75 m person weighing 70 kg has a BMI of 70 ÷ (1.75 × 1.75) = 22.9. In imperial, that's roughly 5 ft 9 in and 154 lb, which the 703 multiplier converts to the same 22.9. This tool switches between them so you can enter whichever measurements you already have without converting by hand.
Frequently asked questions
What is a healthy BMI?
For most adults, a BMI between 18.5 and 24.9 is considered the healthy range. Below that is underweight, 25–29.9 is overweight, and 30 or above is obese.
Is BMI accurate for athletes?
Not always. BMI can't distinguish muscle from fat, so very muscular people often score higher than their body fat would suggest. It's a screening tool, not a body-composition measurement.
How is BMI calculated?
Metric: weight (kg) ÷ height (m)². Imperial: 703 × weight (lb) ÷ height (in)². This tool handles both automatically.
Does this work for children?
Standard BMI categories are for adults. Children and teens use age- and sex-specific percentiles, which this calculator does not compute.
Should I worry if my BMI is one point over 25?
Not on its own. BMI is a broad screen, and the boundaries are not cliffs. Consider your waist size, activity level, and overall health, and speak to a professional rather than reacting to a single point.
Last updated: 2026-01-15