BMI Calculator – Complete Guide & Free Online Tool

A BMI calculator computes your Body Mass Index from your weight and height and places it into a standard category (underweight, normal, overweight, obese). Free online tool included.

Published 2026-09-13

In this guide
  1. What is BMI Calculator?
  2. How BMI is calculated
  3. Limitations
  4. Key Features
  5. Examples
  6. Common Use Cases
  7. Tips & Best Practices
  8. Limitations
  9. Related Tools
  10. External Resources

What is BMI Calculator?

A BMI calculator computes your Body Mass Index from your weight and height and places it into a standard category (underweight, normal, overweight, obese).

How BMI is calculated

BMI = weight (kg) / height (m)². Standard categories: under 18.5 is underweight, 18.5–24.9 normal, 25–29.9 overweight, and 30+ obese.

Limitations

BMI does not distinguish muscle from fat, so very muscular people may be classified as overweight. It is a screening tool, not a direct measure of health.

Key Features

• Accurate BMI formula • Standard categories • Instant results

Examples

• 70 kg at 175 cm → BMI ≈ 22.9 (normal).

Common Use Cases

• Health screening • Fitness tracking • Weight goals

Tips & Best Practices

• Interpret BMI alongside other health indicators • not in isolation.

Limitations

• BMI can misclassify athletes and older adults.

Related Tools

Explore other calculators: [Calculators](/categories/calculators).

Related tools: [age-calculator](/tools/age-calculator), [percentage-calculator](/tools/percentage-calculator), [average-calculator](/tools/average-calculator).

External Resources

WHO: BMI

Related Tools

Age Calculator Calculate your exact age in years, months, weeks and days. Calculators Use Tool →
Percentage Calculator Calculate percentages, increases, decreases and percentage difference. Calculators Use Tool →
Average Calculator Calculate the mean, sum, minimum and maximum of a set of numbers. Calculators Use Tool →

Frequently Asked Questions

What is BMI?
Body Mass Index, a measure of body size based on weight and height.
How is BMI calculated?
Weight in kg divided by height in meters squared.
What are healthy BMI ranges?
18.5–24.9 is considered normal.
Is BMI always accurate?
No, it does not distinguish muscle from fat.
Is it free?
Yes, and it runs locally.

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