BMI Calculator with Metric and Imperial Units
Type in your height and weight, this BMI calculator with metric and imperial units accepts kg/cm or lb/ft, and get your Body Mass Index, the standard weight category, the healthy range for your height and the ideal weight for your height and age. One caveat before you read your number: BMI is a screening figure, not a diagnosis. It cannot see muscle mass, frame size or age, so a gym built 25 and a couch bound 25 are very different things. Uses the standard WHO formula and shows where you sit on the official BMI chart, from underweight through to obese class 3.
Related reading: Guide: what is a healthy BMI?
Last updated: October 22, 2026
Your result
The formula
Metric: BMI = weight (kg) ÷ height (m)²Imperial: BMI = 703 × weight (lb) ÷ height (in)²Categories: under 18.5 underweight, 18.5 to 24.9 healthy weight, 25 to 29.9 overweight, 30+ obesity
A worked example
Someone 170 cm tall weighing 68 kg lands on a BMI of 68 ÷ 1.7² = 23.5, inside the healthy range, which for that height spans roughly 53.5 to 72 kg.
More about the BMI Calculator
What BMI is, and what it is not
Body mass index is a simple screening measure of weight relative to height: weight in kilograms divided by height in metres, squared. For adults the World Health Organization bands do not move, below 18.5 is underweight, 18.5 to 24.9 is the healthy range, 25 to 29.9 is overweight and 30 plus is obesity. It is deliberately basic: a single number that flags the weight categories most linked to health risk.
Basic also means blinkered. BMI cannot separate muscle from fat, so a muscular athlete can land "overweight" while carrying very little fat; it is a poor fit for children, who are assessed against age based percentiles, and it gets fuzzy for the very elderly; Asian adults are interpreted against lower thresholds. By hand, square your height in metres first, then divide your weight in kilos by that number, in pounds and inches, divide weight by height squared and multiply by 703. Or just enter your numbers above and let the calculator show your BMI with the healthy range for your height.
BMI in stones and pounds (UK)
One stone is exactly 14 pounds. To convert: divide your total pounds by 14, 168 lbs is exactly 12 stone. The calculator accepts stones directly, so there is no need to convert first.
UK health guidance uses the same bands as everywhere else: under 18.5 underweight, 18.5 to 24.9 healthy, 25 to 29.9 overweight, 30+ obese. But BMI is a screening tool, not a diagnosis, muscular builds read high, and older adults can read low despite higher body fat.
If you train with weights, pair BMI with a waist measurement. A 32 inch waist on a high BMI lifter tells a very different story than the number alone.
How to use the BMI Calculator
- Choose metric (kg and cm) or imperial (lb, ft and in) units.
- Enter your current weight and height.
- Press Calculate to see your BMI, its category, and the healthy weight range for your height.
Frequently asked questions
Is BMI accurate for everyone?
Not quite. BMI cannot tell muscle from fat, so very muscular people can score high without excess body fat, and it was never designed for children, pregnant women or the very elderly. Treat it as a rough screening number and talk to a healthcare professional for the full picture.
How do I calculate BMI by hand?
Metric: divide your weight in kilograms by your height in metres, squared. Imperial: multiply your weight in pounds by 703, then divide by your height in inches, squared.
How much weight do I need to lose to reach a healthy BMI?
Multiply your target BMI of 24.9 by your height in metres, squared, then subtract that from your current weight. Say you are 90 kg at 1.75 m: your BMI is 29.4, and 24.9 lands at about 76 kg, so roughly 14 kg to lose.
Is BMI interpreted differently for Asian adults?
Yes, several health authorities, including the WHO's Asia Pacific guidance, set lower cutoffs for Asian populations: overweight from BMI 23, obesity from 27.5. The reason is that risks like type 2 diabetes tend to appear at lower BMIs in people of East and South Asian descent.
What's the difference between BMI and body fat percentage?
BMI only relates weight to height, it cannot see whether that weight is muscle or fat, so a rugby player at BMI 28 might be leaner than an office worker at 24. Body fat percentage, taken with calipers, a smart scale or a DEXA scan, shows what you are actually made of; healthy ranges sit around 10 to 20% for men and 18 to 28% for women.
Can I use BMI during pregnancy?
Not as a target, the adult categories were not built for pregnancy, when weight gain is expected and healthy. Doctors instead use your pre pregnancy BMI to set a recommended total gain range; ask your midwife or doctor what fits you.
What BMI percentile is considered healthy for a child?
The CDC defines healthy weight as the 5th percentile up to (but not including) the 85th percentile for a child's age and sex. Below the 5th percentile is underweight, 85th to below 95th is overweight, and at or above the 95th percentile is obesity. These are screening categories, not a diagnosis, a pediatrician interprets them alongside growth history, fitness and family health.
What is a healthy BMI for seniors?
For adults 65 and older, research suggests a healthy BMI of about 23 to 28, slightly higher than the 18.5 to 25 range for younger adults. A little extra weight can protect against frailty and illness in old age. Always confirm with your doctor, since BMI is only one measure.
What is a healthy BMI for adults?
A healthy BMI falls between eighteen point five and twenty four point nine. Below that is underweight, twenty five to twenty nine point nine is overweight, and thirty or above is obese. Check yours with our calculator.
What BMI is considered obese?
A BMI of thirty or higher is classified as obese, with thirty five plus as severe obesity. Health risks rise significantly at these levels. Check your category with our free calculator.