Calculate your Body Mass Index (BMI) and see where you fall on the BMI scale with your healthy weight range.
Your BMI Result
About the BMI Calculator — Calculate Body Mass Index Online Free
Enter your height and weight, click Calculate, and you've got your BMI — along with the healthy weight range for your height. This free BMI calculator works in both imperial (feet, inches, pounds) and metric (centimetres, kilograms) with no account or app required.
Body Mass Index was developed by Belgian mathematician Adolphe Quetelet in the 1830s as a statistical measure of human body proportions. It didn't become a health screening tool until the 1970s, when physiologist Ancel Keys promoted it in an obesity study. The WHO adopted it as a standard diagnostic measure in the 1990s — and despite its well-known limitations, it's still the most common population-level weight assessment method in the world. Understanding what BMI actually measures — and what it doesn't — is what makes the number useful.
How to Use the BMI Calculator
Select Imperial (feet/inches and pounds) or Metric (centimeters and kilograms) to match the units you know your measurements in.
Enter your height and weight accurately. For imperial height, enter feet and inches separately.
Click Calculate BMI to see your result instantly.
View your BMI value, category label, and healthy weight range for your height.
WHO categories: Underweight < 18.5 · Normal weight 18.5–24.9 · Overweight 25–29.9 · Obese Class I 30–34.9 · Obese Class II 35–39.9 · Obese Class III ≥ 40
Measure height without shoes: Footwear adds 1–3 cm (0.5–1 inch) depending on shoe type. Measure against a wall in bare feet for the most accurate height input.
Weigh yourself consistently: Body weight fluctuates by 1–3 kg throughout a single day due to food, water, and clothing. Weigh at the same time each day — ideally in the morning before eating — if you're tracking changes over time.
Understand BMI's limitations for your body type: BMI can't distinguish between fat and muscle. Athletes and strength trainers often land in the "overweight" or "obese" range despite low body fat. If that's you, waist circumference or body fat percentage testing tells a more accurate story.
Use the healthy weight range, not just the category: The calculator shows the actual weight range classified as "normal" for your height. That's often more useful than the label — knowing you're 3 kg above the healthy range is more actionable than knowing you're "overweight."
Consider ethnicity-adjusted thresholds: WHO's standard thresholds were built mainly from European population data. People of South Asian, East Asian, and some other ethnic backgrounds face higher health risks at lower BMI values. Some health authorities recommend lower cutoffs — overweight at 23+ for Asian populations, for example.
Frequently Asked Questions about BMI Calculator
Not really. Muscle is denser than fat, so a muscular person can hit the "overweight" or "obese" range while having very low body fat and excellent cardiovascular health. For athletes, more meaningful measures include body fat percentage (via DEXA scan or skinfold callipers), waist-to-height ratio, or visceral fat assessment. BMI works as a rough population-level screen — it's not a personal fitness assessment.
The WHO defines a healthy BMI for adults as 18.5–24.9. Below 18.5 is underweight, 25–29.9 is overweight, and 30 or above is obese. But the ideal threshold varies a bit by age, ethnicity, and sex — your doctor can put your specific number in context alongside your other health indicators.
The formula is identical, but the health implications aren't quite the same. Women naturally carry more body fat than men at the same BMI value due to hormonal differences — a woman and a man at BMI 23 have the same weight-for-height ratio but different actual body fat percentages. Some researchers argue for sex-specific thresholds, though the standard WHO ranges apply to both sexes equally in clinical practice.
The healthy weight range is calculated by solving the BMI formula for weight at BMI 18.5 (lower bound) and BMI 24.9 (upper bound) using your entered height. At 5'9" (175 cm): minimum healthy weight = 18.5 × 1.75² = 56.7 kg (125 lbs); maximum = 24.9 × 1.75² = 76.3 kg (168 lbs).
Yes — very differently. For ages 2–19, BMI is plotted on age- and sex-specific growth charts as a percentile ranking rather than a fixed category. The 85th–94th percentile is overweight; 95th or above is obese. This calculator uses adult WHO thresholds and shouldn't be used for anyone under 18 — use a paediatric BMI chart instead.
No. BMI is just weight divided by height squared — it can't tell the difference between fat, muscle, bone, or water. Two people with the same BMI can have dramatically different body compositions. It's a population-level screening proxy, not an individual body fat measurement. For direct fat measurement, you'd need DEXA scanning, hydrostatic weighing, or bioelectrical impedance analysis.
Yes — completely free, no account needed. All calculations run in your browser; nothing is stored or sent anywhere. Enter your measurements and click Calculate BMI.
Every 3–6 months is plenty for most people. Daily checks don't make sense — normal weight fluctuations from food and water can shift your number by a meaningful amount without reflecting any real change. If you're actively trying to gain or lose weight, monthly BMI checks alongside waist circumference measurements give you a more complete picture of progress.