BMI Calculator
Calculate body mass index with category range and healthy weight guidance.
What this tool does
Calculate body mass index from height and weight using metric or US customary units.
How to use
- Choose metric or US units.
- Enter your height and weight.
- Review BMI value, category, and healthy weight range.
Formula
BMI = weight (kg) ÷ height (m)²
Examples
Metric example
Input: height=170 cm, weight=70 kg
Output: BMI ≈ 24.2 (Normal)
70 ÷ (1.7²) ≈ 24.2
Learn more
Understanding BMI categories
The World Health Organization (WHO) defines adult BMI ranges as: under 18.5 (underweight), 18.5–24.9 (normal), 25–29.9 (overweight), and 30 or above (obese). These ranges are screening thresholds, not diagnoses.
Your result places you in a category based on height and weight alone. Individual factors like muscle mass, age, and body composition are not reflected in the standard formula.
When BMI can be misleading
BMI does not distinguish fat from muscle. Athletes and very muscular individuals may score in the overweight range despite low body fat.
BMI is not intended for children, pregnant individuals, or certain elderly populations without clinical guidance. Always consult a healthcare provider before making health decisions based on BMI.
What to do after calculating BMI
If you want to set nutrition or weight goals, estimate your daily calorie needs next. Our calorie calculator uses the Mifflin-St Jeor equation and can link directly to macro targets.
Assumptions
- Standard adult BMI formula.
- Not intended for children or pregnancy without clinical guidance.
Common use cases
- Quick body composition screening
- Track weight goals against healthy range
- Estimate healthy weight for your height
FAQ
What is a healthy BMI?
WHO ranges: under 18.5 underweight, 18.5–24.9 normal, 25–29.9 overweight, 30+ obese.
Is BMI accurate for athletes?
BMI does not distinguish muscle from fat. Use with other metrics if you are very muscular.
Is this medical advice?
No. For informational purposes only. Consult a healthcare provider before changing diet or exercise.
How is BMI calculated?
BMI = weight (kg) ÷ height (m)². US units are converted internally before the formula is applied.
What is a normal BMI?
For adults, WHO defines normal BMI as 18.5 to 24.9.
Can I use BMI during pregnancy?
Standard adult BMI ranges are not intended for pregnancy. Follow prenatal care guidance instead.
Does age affect BMI interpretation?
The formula is the same for all adults, but context matters more with age. Older adults may lose muscle while weight stays stable.
What should I do after calculating BMI?
If you want nutrition targets, try the calorie calculator for TDEE estimates, then the macro calculator for protein, carb, and fat splits.
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Last reviewed: 2026-05-23