BMI Calculator
Calculate your Body Mass Index in metric or imperial units. Instant, free.
How to Use
- Step 1: Select Metric (kg/cm) or Imperial (lb/ft·in) using the toggle.
- Step 2: Enter your weight and height.
- Step 3: Your BMI, category, and healthy weight range display instantly.
About BMI Calculator
Body Mass Index (BMI) is a widely used screening tool to categorize individuals based on their weight relative to height. The formula is simple: BMI = weight (kg) ÷ height² (m²). For imperial measurements, the tool automatically converts pounds to kilograms and feet/inches to meters before calculating.
The WHO classifies BMI into four main categories: Underweight (below 18.5), Normal weight (18.5–24.9), Overweight (25.0–29.9), and Obese (30.0 and above). The calculator also shows the healthy weight range for your specific height — the weight range that would put you in the normal BMI category.
Important caveat: BMI is a population-level screening tool, not a diagnostic measure. Muscular athletes, pregnant women, and the elderly may get misleading BMI readings. Always consult a healthcare professional for proper assessment.
You may also find our Weight Converter, Length Converter, and Percentage Calculator helpful.
Frequently Asked Questions
What is BMI?
Body Mass Index (BMI) is a measure of body fat based on height and weight. It is used to broadly categorize individuals into underweight, normal, overweight, and obese.
What is a healthy BMI range?
A BMI between 18.5 and 24.9 is considered normal weight for adults. Below 18.5 is underweight; 25–29.9 is overweight; 30+ is obese.
Is BMI accurate for everyone?
BMI is a screening tool, not a diagnostic. It does not account for muscle mass, bone density, age, or ethnicity. Athletes often have high BMI despite low body fat.
How do I convert height?
1 foot = 12 inches. 1 inch = 2.54 cm. For example, 5'9" = 69 inches = 175.26 cm.
Does BMI apply to children?
BMI for children (2–19 years) uses age- and gender-specific percentile charts, which are different from adult BMI categories.
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Guide
How to calculate and read your body mass index (BMI)
Body mass index compares your weight with your height using one formula: weight in kilograms divided by height in metres squared. This calculator lets you choose Metric (kg / cm) or Imperial (lb / ft·in), converts imperial entries behind the scenes, and displays three results: the BMI to one decimal place, a category label, and a Healthy Range showing the weights that would fall in the 'Normal weight' band for your height.
BMI is a quick screening number, not a diagnosis, and this page is informational only. It does not know your age, sex, muscle, frame size or health history. Treat it as one rough data point and a prompt for a conversation with a doctor or dietitian.
Step by step
- Press Metric (kg / cm) or Imperial (lb / ft·in). The two modes keep separate values, so switching does not convert what you typed.
- In metric mode type Weight (kg) and Height (cm). In imperial mode type Weight (lbs), Height (ft) and Height (in) in three boxes.
- Read the BMI box. It updates as you type and is rounded to one decimal.
- Look at the Category box, which says Underweight, Normal weight, Overweight or Obese, then at Healthy Range for the weights that would fit the Normal weight band at your height.
- Compare with the strip of four reference bands below: under 18.5, 18.5 to 24.9, 25 to 29.9, and 30 and above.
When this is useful
- Getting a rough starting point before a routine health check-up.
- Seeing what weight range corresponds to the Normal weight band at your height when setting a fitness goal.
- Checking a conversion between kilograms and pounds without separate arithmetic.
- Understanding what a BMI figure on a lab report or fitness app means.
Worked example: A 62 kg adult who is 162 cm tall
In Metric mode enter 62 for weight and 162 for height. Height in metres is 1.62, and 1.62 squared is 2.6244. Dividing 62 by 2.6244 gives 23.6, shown as BMI 23.6 with the category Normal weight. The Healthy Range reads 48.6 – 65.3 kg, which is 18.5 and 24.9 multiplied by 2.6244. In Imperial mode the starting values of 154 lbs and 5 ft 9 in give a BMI of 22.7 and a range of 125.2 – 168.7 lbs.
Tips for better results
- Measure height without shoes and weight at a similar time of day to compare readings fairly.
- Check the unit labels. Height here is in centimetres in metric mode; typing 1.75 will give an absurdly high BMI.
- In imperial mode the inches box can exceed 11; the tool computes feet times 12 plus inches, so 0 ft and 69 in works the same as 5 ft 9 in.
- Use Healthy Range as a reference band, not a target. Individual healthy weights vary within and outside it.
Common mistakes
- Treating the category as a diagnosis. The labels are broad population bands. A person with a lot of muscle can land in Overweight, while someone with little muscle can sit in Normal weight and still have health risks.
- Using it for children, teenagers or pregnancy. The categories shown are the adult bands. Children are assessed on age- and sex-specific growth charts, and pregnancy changes weight for reasons BMI cannot capture.
- Assuming it applies region-specific thresholds. The tool uses only the standard adult cut-offs of 18.5, 25 and 30. Some guidelines for Asian populations suggest lower cut-offs for health risk, so people of South Asian origin should ask a doctor which thresholds apply to them.
- Entering zero or leaving a box empty. The result then shows a BMI of 0 and the label Underweight, which means nothing. Enter both height and weight.
Your files and privacy
Your height and weight are processed in your browser. This tool does not send them to a server and does not save them between visits; the numbers disappear when you close or reload the page.
Frequently asked questions
What formula does the calculator use?
BMI equals weight in kilograms divided by the square of height in metres. In imperial mode pounds are multiplied by 0.453592 and feet-and-inches are converted to metres using 0.0254 per inch before the same formula runs.
Which BMI categories does it show?
Underweight below 18.5, Normal weight from 18.5 to under 25, Overweight from 25 to under 30, and Obese at 30 and above. There are no sub-classes of obesity and no separate thresholds for particular ethnic groups.
Why is my Healthy Range slightly different from what I calculated by hand?
The upper end uses 24.9 rather than 25, and in imperial mode the kilogram figures are rounded to one decimal before being converted to pounds. Differences are small, usually a few tenths of a kilogram.
Is BMI accurate for athletes or older adults?
It can mislead. Muscle weighs more than fat, so a muscular person may read high, and older adults who have lost muscle may read normal. Waist measurement and body composition tests tell a doctor more.
Should I change my diet or exercise because of this number?
This page is informational and not medical advice. A doctor or registered dietitian can interpret your BMI alongside blood tests, family history and lifestyle, and advise on whether any change is appropriate.
Guide reviewed 2026-10-11 by the useToolify team.
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