Enter your weight and height in metric or imperial. Get your Body Mass Index, category, BMI Prime, healthy weight range, and an animated visual scale — all instantly.
Metric & imperial BMI category BMI Prime Healthy weight range Animated visual scale Weight-to-target tip
BMI Calculator — Body Mass Index, Categories & Healthy Weight Range
This free BMI calculator uses your weight and height to compute your Body Mass Index, classify it into one of four WHO categories, and show how far you are from the healthy range. Both metric (kg/cm) and imperial (lb/ft·in) units are supported — enter your measurements, click calculate, and results appear instantly with a visual progress bar that shows exactly where you sit on the BMI scale.
The calculator also shows your BMI Prime (a ratio that makes it easy to see how far above or below the healthy boundary you are), your healthy weight range for your height, and the exact weight gain or loss needed to reach the healthy zone.
How BMI Is Calculated
The BMI formula is straightforward — weight divided by the square of height:
Height must be converted to meters (metric) or total inches (imperial) before squaring.
Example: Person weighs 75 kg, height 175 cm (1.75 m)
BMI = 75 ÷ (1.75²) = 75 ÷ 3.0625 = 24.5 — Normal weight
BMI Categories — WHO Standard
The World Health Organization defines four BMI categories for adults:
UnderweightBMI < 18.5May indicate malnutrition, eating disorders, or underlying illness. Associated with increased risk of bone loss, immune suppression, and infertility.
Normal Weight18.5 – 24.9Associated with the lowest risk of weight-related health conditions. Most health guidelines aim to maintain BMI within this range.
Overweight25.0 – 29.9Increased risk of cardiovascular disease, type 2 diabetes, and high blood pressure. Modest weight reduction (5–10%) can meaningfully reduce health risk.
ObeseBMI ≥ 30.0Significantly elevated risk of serious conditions including heart disease, stroke, type 2 diabetes, sleep apnea, and certain cancers. Medical guidance is recommended.
What Is BMI Prime?
BMI Prime is your BMI expressed as a ratio relative to the upper boundary of the healthy BMI range (25.0). It makes it visually clear how close to — or far from — the healthy boundary you are:
BMI Prime
Meaning
Corresponds to
< 0.74
Underweight
BMI below 18.5
0.74 – 1.00
Normal weight
BMI 18.5 – 25.0
1.00 – 1.20
Overweight
BMI 25.0 – 30.0
> 1.20
Obese
BMI above 30.0
BMI Prime of exactly 1.00 means you're at precisely the upper edge of the healthy range. A value of 1.15 means your BMI is 15% above that threshold — easy to interpret at a glance without needing to memorise category cutoffs.
BMI Limitations — What It Doesn't Tell You
BMI is a useful population-level screening tool, but it has significant limitations for individuals:
Muscle MassHighly muscular athletes often have a "overweight" BMI despite low body fat. Muscle is denser than fat — BMI cannot distinguish the two.
Age & GenderOlder adults naturally lose muscle and gain fat, so BMI can underestimate health risk. Women also tend to carry more body fat than men at the same BMI.
EthnicityAsian populations have higher health risk at lower BMI thresholds. Many Asian health guidelines use adjusted cutoffs (≥23 = overweight, ≥27.5 = obese).
Height ExtremesBMI tends to overestimate body fat in taller people and underestimate it in shorter people due to the non-linear relationship between height and body volume.
Professional guidance: BMI is a starting point, not a diagnosis. For a complete health assessment, consult a doctor who can evaluate waist circumference, body fat percentage, blood pressure, cholesterol, and lifestyle factors together.
How to Use This BMI Calculator
Select your gender — used to tailor the healthy weight tip shown in results.
Choose your unit system — Metric (kg/cm) or Imperial (lb, ft/in).
Enter your weight — in kilograms (metric) or pounds (imperial).
Enter your height — in centimetres (metric) or feet and inches (imperial).
Click "Calculate BMI" — results appear with an animated progress bar, your category, BMI Prime, healthy weight range, and a weight-to-target note.
Frequently Asked Questions
The WHO defines a healthy BMI range as 18.5 to 24.9 for adults. Below 18.5 is underweight; 25–29.9 is overweight; 30 and above is obese. These thresholds apply to most adults regardless of age or gender, though some ethnic groups have different risk thresholds.
Metric: BMI = weight(kg) ÷ height²(m). Imperial: BMI = 703 × weight(lb) ÷ height²(in). For example, someone weighing 80 kg at 180 cm has BMI = 80 ÷ (1.80²) = 80 ÷ 3.24 = 24.7.
BMI Prime is your BMI divided by 25 (the upper healthy limit). A BMI Prime of 1.0 means you're exactly at the boundary between normal and overweight. Below 1.0 = normal or underweight; above 1.0 = overweight or obese. It's a simple decimal that shows your position relative to the healthy boundary.
Yes. BMI cannot distinguish muscle from fat, so athletes and very muscular people often show as overweight despite being healthy. It also doesn't account for fat distribution — two people with the same BMI can have very different health risks depending on where they store fat (waist vs. hips).
The standard BMI categories (18.5–24.9 normal) apply equally to both men and women. However, at the same BMI, women typically carry about 10% more body fat than men. Some clinicians use slightly different body fat targets by gender, but BMI thresholds themselves are not gender-differentiated in WHO guidelines.
Standard adult BMI categories do not apply to children and teens. For those under 18, BMI-for-age percentile charts (CDC or WHO) are used instead — they account for the fact that healthy body fat changes significantly with age and development. This calculator is designed for adults.
After calculating your BMI, the results show your healthy weight range for your height and the exact kilograms or pounds you'd need to gain or lose to enter the normal range. Remember that gradual weight change (0.5–1 kg/week) is generally safer and more sustainable than rapid loss.
Standard BMI can misclassify athletes as overweight due to high muscle mass. A 90 kg athlete at 180 cm has BMI = 27.8 (overweight), yet may have very low body fat. For athletes, body fat percentage measurement (DEXA scan, skinfold calipers) is a more accurate health indicator than BMI.
