BMI (Body Mass Index) is a quick screening number that relates your weight to your height. It's not a full health assessment, but it's the standard starting point used by doctors, insurers, and fitness trackers worldwide.
Calculate yours in seconds, no account needed: Free BMI Calculator — Metric & Imperial
How to Use the Calculator
- Go to the BMI Calculator
- Choose your unit system — Metric (kg + cm) or Imperial (lbs + inches/feet)
- Enter your height and weight
- Your BMI and category appear instantly
No submit button. No waiting. The result updates as you type.
The BMI Formula
Metric:
BMI = weight (kg) ÷ height (m)²
Imperial:
BMI = (weight (lbs) × 703) ÷ height (inches)²
Example (metric): 70kg, 175cm → 70 ÷ (1.75 × 1.75) = 22.9
BMI Categories (WHO Standard)
| BMI Range | Category |
|---|---|
| Under 18.5 | Underweight |
| 18.5 – 24.9 | Normal weight |
| 25.0 – 29.9 | Overweight |
| 30.0 – 34.9 | Obese (Class I) |
| 35.0 – 39.9 | Obese (Class II) |
| 40.0 and above | Obese (Class III) |
The calculator shows which category your result falls in and colour-codes it for quick reading.
What BMI Does Not Tell You
BMI is a useful screening number but has well-known limitations:
It does not account for muscle mass. A professional athlete with high muscle mass and low body fat can register as "overweight" by BMI. Muscle weighs more than fat per unit volume.
It does not distinguish fat distribution. Carrying weight around the abdomen (visceral fat) is more metabolically risky than the same weight in the legs or arms. BMI does not capture this.
It varies by ethnicity. Some populations have different risk thresholds. Many clinical guidelines use a lower obesity cutoff (BMI 27.5 instead of 30) for people of Asian descent.
It does not account for age. Older adults naturally have higher body fat percentage at the same BMI compared to younger adults.
Use BMI as one signal among several — not the only one.
What to Do With Your Result
Normal (18.5–24.9): No immediate weight-related action needed. Focus on maintaining through consistent diet and activity.
Overweight (25–29.9): A modest reduction of 5–10% of body weight has documented benefits for blood pressure, blood sugar, and cholesterol levels.
Underweight (under 18.5): Worth discussing with a doctor. Underweight can signal nutritional deficiency or underlying conditions.
Obese (30+): Typically the threshold at which doctors recommend structured lifestyle intervention or, in some cases, medication or surgery.
None of this replaces a conversation with a healthcare provider. BMI is the first number, not the last word.
Metric vs Imperial — Which Should You Use?
Use whatever your measurement system is. The calculator supports both, and the result is identical regardless of which you enter (it converts internally).
If you have a bathroom scale in pounds and measured your height in feet and inches — use Imperial. No conversion needed.
Calculate your BMI now: Free BMI Calculator — Metric and Imperial
No account. No data sent to a server. Results are instant and stay on your screen only.
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