← All posts
BMI Calculator: Check Your Body Mass Index Instantly
Body Mass Index is the quickest health screening number there is — a simple ratio of weight to height used by doctors, gyms, and insurers. A BMI calculator gives you the number and its category in seconds, in metric or imperial. Here's how it works, what it means, and its limits.
How BMI is calculated
- Metric — weight (kg) ÷ height (m)²
- Imperial — (weight (lb) ÷ height (in)²) × 703
Calculate your BMI free with Tooly
The Tooly BMI Calculator makes it instant:
- Enter your weight and height — metric or imperial
- Get your BMI and category immediately
- Runs in your browser — nothing is uploaded
- Free, no signup, no limits
Calculate your BMI free — no signup
Open BMI Calculator
Open BMI Calculator
BMI categories
| BMI | Category |
|---|---|
| Below 18.5 | Underweight |
| 18.5 – 24.9 | Normal weight |
| 25 – 29.9 | Overweight |
| 30 – 34.9 | Obesity (Class I) |
| 35 – 39.9 | Obesity (Class II) |
| 40+ | Obesity (Class III) |
What BMI does and doesn't tell you
- Good screening tool — cheap, instant, and correlates with population health trends
- Doesn't measure body fat directly — athletes with high muscle mass often show "overweight"
- Doesn't consider age, sex, or body composition — use it as a starting point, not a verdict
- Pair with other signals — waist circumference, bloodwork, and how you feel matter more
Frequently Asked Questions
Is this BMI calculator really free? Yes — unlimited use, no account, no limits.
Is my data private? Everything runs in your browser — your measurements never leave your device.
Is BMI accurate for athletes? No — it can misclassify muscular people. Use it as a general screen, not a diagnosis.
What else should I check? The Age Calculator and Unit Converter pair well for health tracking.