This adult BMI screening tool is intended for people age 20 and older. The formula uses weight and height only.
Calculation details
Adult screening estimate only, not a diagnosis. Body composition, age, pregnancy, medical history, and population-specific risk can change interpretation; discuss health decisions with a qualified clinician.
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Use this result
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What does this calculator estimate?
A BMI calculator estimates body mass index from height and weight. Enter the numbers to see your BMI and category.
- BMI = kg ÷ m² (or lb ÷ in² × 703)
- 18.5–24.9 = healthy range
- A screen, not a body-fat measure
What BMI measures
BMI relates weight to height as a population screening tool. It correlates with body fat for most people and predicts health risk at the extremes. Ranges are set by WHO standards, with lower thresholds for some Asian populations.
Limitations to watch for
BMI doesn't distinguish muscle from fat — an athlete can be 'overweight' with low body fat. It ignores age, sex, and body composition. Use it as a first screen, then measure waist and body fat for the full picture.
How to use it in practice
Enter height and weight to see your category. Track it alongside waist circumference and strength/energy. If BMI is high, body-fat percentage is the better metric to confirm the risk.
['Enter height and weight.', 'Read the BMI and category.', 'Confirm with body fat if borderline.']
How this calculator works
Formula
BMI = weight (kg) ÷ height (m)², or weight (lb) ÷ height (in)² × 703. Categories: <18.5 underweight, 18.5–24.9 healthy, 25–29.9 overweight, 30+ obese.
Worked example
170 lb at 5'9": BMI = 170 ÷ 69² × 703 = 25.1 — top of the healthy range.
Assumptions to verify
- Height and weight are entered accurately.
- WHO category thresholds apply.
- The result is used as a screening tool.
Frequently asked questions
How do I calculate BMI?
Weight (kg) ÷ height (m)² — or lb ÷ in² × 703: 170 ÷ 69² × 703 = 25.1.
What is a healthy BMI?
18.5–24.9; under 18.5 is underweight, 25–29.9 overweight, 30+ obese.
Is BMI accurate for athletes?
No — it doesn't distinguish muscle from fat, so muscular people read as overweight.
Does BMI work for children?
Yes, with age/sex percentiles — adult categories don't apply.
What's better than BMI?
Body fat percentage, waist circumference, and waist-to-hip ratio add the missing information.
Why do thresholds differ by ethnicity?
Some Asian populations face higher risk at lower BMI — WHO has adjusted guidance.
Is BMI a diagnosis?
No — it's a screening number. Health assessment considers many factors.
Cite this tool
BoringToolsKit. “BMI Calculator.” boringtoolskit.com/bmi-calc/ (reviewed 2026-08-25). Free to reference in articles, syllabi, and answer posts with a link.
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