Health Calculator
BMI Calculator
Calculate your body mass index using height and weight, then read the result as a simple screening estimate.
What this calculator does
The BMI Calculator estimates Body Mass Index from height and weight. BMI is a screening number used to describe whether a person is broadly within underweight, normal, overweight, or obesity ranges. The calculator converts height from centimeters to meters and divides weight by height squared.
After you enter height and weight, the tool computes the index and places it on the standard adult scale: under 18.5 underweight, 18.5–24.9 normal, 25–29.9 overweight, and 30+ obesity. The number is a population-level screening statistic — it says how your weight compares for your height, not how healthy you are.
When to use it
Use it when starting a fitness plan, tracking a general health goal, or checking a first weight-to-height reference. It is useful for adults, but athletes, children, pregnant people, older adults, and people with high muscle mass may need additional assessment.
It is a reasonable first reference when starting a fitness plan or tracking gradual weight change over months. It is a poor tool for muscular athletes (muscle weighs more than fat), growing children and teens (who need age-specific percentile charts), pregnant women, and adults over about 65. This page is educational and is not medical advice.
Formula used
BMI = weight in kilograms / (height in meters x height in meters).
Because height is squared in the denominator, small height errors distort the result twice over: entering 165 cm instead of 170 cm shifts the BMI of a 70 kg person from 24.2 to 25.7 — across a category boundary. Measure height without shoes and enter weight in kilograms for the formula to work as designed.
Understanding each input
- Height in centimetres — measured without footwear. The calculator converts to metres internally; if you know your height in feet and inches, convert first (5′7″ ≈ 170 cm).
- Weight in kilograms — ideally measured at a consistent time of day, since normal daily fluctuation of 1–2 kg can move the result noticeably.
Example calculation
If a person weighs 70 kg and is 170 cm tall, height is 1.70 meters. BMI = 70 / (1.70 x 1.70) = 24.2, commonly within the normal adult BMI range.
The example person at 24.2 sits near the top of the normal range — a useful illustration that BMI categories are bands with hard edges, not verdicts. A change of less than 3 kg would move this person into a different label without any meaningful change in health.
Benefits
- Get a quick screening number
- Track broad changes over time
- Use metric inputs easily
- Understand BMI limits
- Prepare for a health discussion
The most defensible use is tracking your own trend: because your height is constant, BMI changes map directly to weight changes, and a slow drift across months is easier to see in one number than in daily scale readings that bounce around.
Reading the result
Read the number as a zone, not a verdict. Within 1 point of a boundary, measurement noise alone could place you on either side. What deserves attention is a sustained move across categories over months, or a value far from the normal band — both are conversation starters with a clinician, alongside better measures like waist circumference and blood work.
Assumptions and limitations
BMI cannot distinguish fat from muscle, does not measure fat distribution (waist-centred fat carries different risk), and applies adult thresholds that are not valid for children or during pregnancy. Some populations use adjusted cut-offs — several Asian health bodies treat 23+ as overweight. A normal BMI does not rule out metabolic issues, and a high BMI in a strength athlete may be perfectly healthy.
Educational screening tool only — not medical advice, diagnosis, or treatment. Discuss weight and health decisions with a qualified clinician.
Common mistakes
- Entering height in feet or inches into a centimetre field — a 5.7 entry produces an absurd result.
- Weighing with shoes, heavy clothing, or right after a large meal and comparing against an old reading taken differently.
- Treating a single category label as a diagnosis rather than a screening flag.
- Applying adult cut-offs to a child or teenager.
FAQs
Is BMI accurate for everyone?
No. BMI is a screening estimate and may be less useful for athletes, children, pregnant people, and some older adults.
What BMI range is normal?
For many adults, 18.5 to 24.9 is commonly considered normal, but medical context matters.
Can BMI measure body fat directly?
No. BMI does not directly measure body fat, muscle, bone density, or body composition.
Should I make medical decisions from BMI alone?
No. Use it as a starting point and consult a qualified professional for personal advice.
Why use centimeters and kilograms?
Metric inputs make the standard BMI formula simple to apply.
AdSense review note
BMI is calculated from the standard weight divided by height-squared formula. The page avoids diagnosis claims and tells users to verify health decisions with qualified medical guidance, especially for children, pregnancy, athletes, or medical conditions. See the editorial standards and site disclaimer for the review process and safety limits.
Related calculators
Continue with tools commonly used with the BMI Calculator.