What BMI means
BMI is weight in kilograms divided by height in meters squared. It is a quick screening number, not a diagnosis. Athletes, children, older adults and pregnant people may need more context than BMI alone.
BMI calculator
Calculate body mass index from height and weight.
Result
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Reading BMI with context
Adult screening ranges
BMI is commonly grouped into underweight, normal range, overweight and obesity categories for adults. It is useful for a quick population-level screen, but it does not directly measure body fat, muscle mass, waist size, age, sex or health conditions.
When BMI can be misleading
A muscular athlete can have a high BMI without the same risk profile as someone with more body fat. Children, teenagers, pregnant people and older adults often need age-specific or clinical interpretation instead of a simple adult BMI label.
Use it as a conversation starter
The result can help you decide whether to look more closely at health habits, measurements or a professional checkup. It should not be used alone to diagnose a condition, set a diet, or decide medication or treatment.
BMI formula
BMI = weight (kg) ÷ height (m)²
Imperial: BMI = 703 × weight (lb) ÷ height (in)²
Adult categories (WHO): under 18.5 underweight · 18.5–24.9 normal · 25–29.9 overweight · 30+ obese
How this calculator works
CalcBloom converts your height and weight to metric, divides weight by height squared, and compares the result to the WHO adult categories — all in your browser. BMI is a quick screening number, not a diagnosis: it does not measure body fat directly and can misjudge athletes, children, pregnancy and older adults. Nothing you enter is uploaded.
Last reviewed: 2026-07
Frequently asked questions
What is a normal BMI?
The common adult range is 18.5 to 24.9.
Is BMI a medical diagnosis?
No. It is a screening tool and should not replace professional advice.
Are my height and weight saved?
No. All calculations happen locally in your browser.
Does BMI work for athletes?
It can be less useful for very muscular people because BMI cannot distinguish muscle from fat. Other measurements may give better context.
Can children use the same BMI ranges?
Children and teenagers are usually interpreted with age- and sex-specific growth charts, not only the adult BMI ranges shown here.
Should I make health decisions from BMI alone?
No. BMI is a simple screening number. For health decisions, consider professional advice and other context such as waist measurement, history and symptoms.