BMI Calculator
This free BMI calculator works out your Body Mass Index from your height and weight, in either metric or US units, and shows which standard weight category it falls into. Nothing you enter is sent anywhere or stored.
How to Use It
- Choose US / Imperial or Metric units.
- Enter your height and weight.
- Your BMI and weight category appear instantly as you type.
How It Works
BMI is calculated as weight in kilograms divided by height in meters, squared. If you enter feet, inches, and pounds instead, those values are converted to kilograms and meters first, so both unit systems always produce the same result for the same body size.
Formula
BMI = weight (kg) ÷ height (m)^2
For example, someone who is 170 cm (5'7") tall and weighs 65 kg (about 143 lb) has a BMI of 65 ÷ (1.7 × 1.7) = 65 ÷ 2.89 ≈ 22.5, which falls in the "normal weight" category below. The same calculation works in reverse for US units: 65 kg and 170 cm convert to roughly 143 lb and 5'7", and produce the identical 22.5 result either way, since both paths run through the same formula once units are normalized.
The result is matched against the standard adult BMI categories. These cutoffs come from the CDC and WHO and are widely used as a general screening measure, not a diagnosis.
| BMI | Category |
|---|---|
| Below 18.5 | Underweight |
| 18.5 to 24.9 | Normal weight |
| 25 to 29.9 | Overweight |
| 30 and above | Obese |
BMI is a useful first screening number, but it only ever measures the ratio of weight to height, not body composition. For a deeper look at where the formula came from and where it breaks down for individual bodies, see our guide, BMI Explained: What It Measures, and Where It Falls Short.
Everything runs client-side in your browser. No measurements you enter are sent anywhere or stored.
Frequently Asked Questions
Is BMI accurate for everyone?
No. BMI only looks at height and weight, so it doesn't distinguish muscle from fat. Very muscular people can show a high BMI despite low body fat, and it isn't a reliable measure for pregnant women or for children (who need age and sex-specific growth charts instead). It's best treated as a general screening number, not a diagnosis. See our BMI guide below for a fuller explanation of where the formula holds up and where it doesn't.
How is BMI calculated?
BMI equals weight in kilograms divided by height in meters, squared. If you enter measurements in feet, inches, and pounds instead, this calculator converts them to kilograms and meters first, then applies the same formula, so the result is identical either way.
What's considered a healthy BMI range for adults?
18.5 to 24.9 is classified as "normal weight" under the standard adult BMI categories used by the CDC and WHO. Below 18.5 is underweight, 25 to 29.9 is overweight, and 30 and above is obese. These cutoffs are population averages, not a guarantee about any one person's health.
Does BMI account for muscle mass?
No. BMI only has two inputs, height and weight, so it can't tell muscle from fat. A muscular, low-body-fat athlete and a sedentary person of the same height and weight get the exact same BMI, even though their actual health profiles can be very different. Waist circumference or a direct body fat measurement are better indicators of body composition specifically.
Is the BMI scale different for men and women?
No. The standard adult BMI categories use the same cutoffs for men and women. BMI doesn't adjust for sex-based differences in typical body composition, which is one of the reasons it's treated as a screening tool rather than a precise individual health measure.
Are BMI categories the same worldwide?
Mostly, but not entirely. The standard 18.5/25/30 cutoffs used here come from CDC/WHO guidance for the general adult population, but the WHO itself recommends lower overweight/obese cutoffs for many Asian populations (overweight starting around 23 rather than 25), since health risk at a given BMI has been shown to vary by ethnicity.
What should I do if my BMI is outside the normal range?
Treat it as a starting point for a conversation, not a verdict. A BMI outside 18.5 to 24.9 is worth discussing with a doctor, especially alongside other factors like waist circumference, activity level, and family health history, since BMI alone can't distinguish the specific cause or whether it reflects excess fat, muscle mass, or something else entirely.