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Free BMI Calculator

Calculate your Body Mass Index (BMI) in metric or imperial units and see which World Health Organization weight category it falls into.

Your BMI
22.9Normal

WHO range for “Normal”: 18.5 – 24.9. BMI is a general indicator, not a diagnosis.

Estimate only. This tool is for general information only and is not medical advice or a diagnosis. Results are estimates based on the formula shown. Consult a qualified healthcare professional for guidance about your own situation.

Quick answer

BMI is your weight divided by the square of your height. In metric units, BMI = weight (kg) ÷ height (m)². In imperial units, BMI = 703 × weight (lb) ÷ height (in)². The WHO ranges are: under 18.5 underweight, 18.5–24.9 normal, 25–29.9 overweight, and 30 or more obese.

Formula & method

Metric

BMI = weight(kg) ÷ height(m)²
  • weight — body weight in kilograms
  • height — height in meters

Imperial

BMI = 703 × weight(lb) ÷ height(in)²
  • 703 — unit conversion factor for pounds and inches

WHO categories: <18.5 underweight, 18.5–24.9 normal, 25–29.9 overweight, ≥30 obese.

BMI categories for adults (WHO)

BMI rangeCategory
Below 18.5Underweight
18.5 – 24.9Normal weight
25.0 – 29.9Overweight
30.0 and aboveObesity

Examples

Example 1: 70 kg, 175 cm
Input
weight = 70 kg, height = 1.75 m
Result
BMI 22.9 — Normal
Why
70 ÷ (1.75 × 1.75) = 70 ÷ 3.0625 = 22.86.
Example 2: 150 lb, 5 ft 6 in
Input
weight = 150 lb, height = 66 in
Result
BMI 24.2 — Normal
Why
703 × 150 ÷ (66 × 66) = 105,450 ÷ 4,356 = 24.21.
Example 3: 90 kg, 170 cm
Input
weight = 90 kg, height = 1.70 m
Result
BMI 31.1 — Obese
Why
90 ÷ (1.70 × 1.70) = 90 ÷ 2.89 = 31.14.

When to use this tool

  • Getting a quick, general sense of where your weight sits relative to your height.
  • Tracking a rough trend over time alongside other measures.
  • As a starting point for a conversation with a healthcare professional.

Common mistakes

  • Entering height in centimeters where meters are expected. 175 cm is 1.75 m.
  • Treating BMI as a body-fat measurement. It’s only a ratio of weight to height.
  • Applying adult BMI ranges to children, who use age- and sex-specific percentiles instead.

Frequently asked questions

What is BMI?

Body Mass Index is a simple ratio of weight to height (weight divided by height squared). It’s used as a rough screening indicator for weight categories across a population.

What is a healthy BMI?

The World Health Organization considers 18.5 to 24.9 the normal range for most adults. Below 18.5 is underweight, 25–29.9 is overweight, and 30 or above is obese.

Is BMI accurate for everyone?

No. BMI doesn’t distinguish muscle from fat or account for body composition, so it can misclassify athletes, older adults, and others. It’s a general indicator, not a diagnosis.

Does BMI work for children?

Not directly. Children and teens are assessed with age- and sex-specific BMI percentiles rather than the fixed adult ranges.

What’s the difference between the metric and imperial formulas?

They give the same result; the imperial version just includes the factor 703 to convert pounds and inches into the same scale as kilograms and meters.

Is this medical advice?

No. This tool is for general information only and is not a diagnosis. Talk to a qualified healthcare professional about your health.

Sources & references

External references open in a new tab. We are independent and not affiliated with these organizations.

Disclaimer

This tool is for general information only and is not medical advice or a diagnosis. Results are estimates based on the formula shown. Consult a qualified healthcare professional for guidance about your own situation.

  • ✓ Free to use
  • ✓ No sign-up required
  • ✓ Runs entirely in your browser — nothing is uploaded.
  • ✓ Formula and method shown above
Last updated: How we calculateReport a correctionDisclaimer

Provided “as is” for general information only — results may be inaccurate, so verify before you rely on them. No warranty; use at your own risk.

Built and reviewed by HIFreeTools against the formula shown above and any authoritative references cited on this page. See our methodology and editorial standards.

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