BMI Calculator: Body Mass Index and Healthy Weight Range from Height and Weight
Free online BMI (Body Mass Index) calculator with an instant metric/imperial toggle. Enter your height and weight to see your BMI on a color-coded gauge, your WHO weight category (underweight to obese class III), your healthy weight range, and the kg to gain or lose. Results update live and can be saved to local history — all computed privately in your browser.
Enter height & weight
BMI = weight(kg) ÷ height(m)²
BMI result
WHO adult standard (18.5–24.9 is normal)
How to Use
Body Mass Index (BMI) Guide
WHO standards · healthy weight range
BMI (Body Mass Index) is the most widely used weight screening metric, proposed in the 19th century by Adolphe Quetelet. It divides weight (kg) by the square of height (m) to produce a dimensionless number that quickly classifies adults as underweight, normal, overweight or obese. FinCompute instantly outputs your BMI, WHO classification and the healthy weight range for your height (18.5–24.9). Everything runs locally — ideal for weight management, interpreting checkups and setting fitness goals.
01 Understanding the BMI categories
The World Health Organization (WHO) classifies adult BMI as: underweight below 18.5, normal 18.5–24.9, overweight 25.0–29.9, and obese at 30.0 and above (further split into classes I–III). These cut-offs are based mainly on European populations; Asian populations — including Chinese — can show metabolic risk at lower BMI, so Chinese guidelines use 24/28 for overweight/obesity.
BMI is quick but cannot distinguish muscle from fat: strength athletes, pregnant women, older adults and people with muscle wasting may be misclassified. Always combine it with body fat percentage, waist circumference and waist-to-hip ratio rather than relying on BMI alone.
- Formula: BMI = weight(kg) ÷ height(m)²
- Lower healthy weight = 18.5 × height(m)²; upper = 24.9 × height(m)²
- Chinese adult overweight reference cut-off is BMI ≥ 24, obese ≥ 28
- Pregnant women, athletes and adults over 65 should also use body fat and circumference measures
02 Metric vs. imperial units
The calculator supports metric (cm/kg) and imperial (ft-in/lb). When you enter 5 ft 7 in and 143 lb, the values are converted to 170 cm and 65 kg before calculation, so both unit systems produce the same BMI. In imperial the formula is BMI = weight(lb) ÷ height(in)² × 703, which the tool applies automatically.
Inputs
- Metric / ImperialSwitches between cm/kg and ft-in/lb input fields.
- heightYour height (cm in metric, feet + inches in imperial).
- weightYour weight (kg in metric, pounds in imperial).
Actions
- CalculateBMI, category and healthy range update live as you type; this button saves the result to the history drawer.
- ResetRestores the default inputs.
- BMI is a screening tool, not a diagnosis; consult a doctor or dietitian about your specific health
- Muscular people may have a high BMI but low body fat, which is healthy
- Waist ≥ 90 cm (men) / 85 cm (women) suggests central obesity risk (Chinese standard)
- Weigh yourself in the morning, fasted and in light clothing to reduce fluctuations
- Children and teens should use age- and sex-specific BMI percentile charts, not adult cut-offs
- A safe rate of weight loss is 0.5–1 kg per week; faster loss tends to rebound
BMI (Body Mass Index) is the most widely used screening metric for healthy weight from height and weight. Enter your height and weight to instantly get your BMI and WHO adult category (underweight through obese class III), the healthy weight range in kilograms for your height, and the amount to gain or lose. Switch between metric cm/kg and imperial ft/lb.
How BMI is calculated
Metric: BMI = weight(kg) ÷ height(m)². Imperial: BMI = weight(lb) ÷ height(in)² × 703. For example, 1.70 m and 65 kg gives 65 ÷ 1.70² ≈ 22.5, which is normal. The tool handles all unit conversion automatically.
WHO adult BMI categories
Under the World Health Organization standard, below 18.5 is underweight, 18.5–24.9 normal, 25–29.9 overweight, 30–34.9 obese class I, 35–39.9 obese class II, and 40 or above obese class III. Chinese adult cut-offs are stricter at 24 for overweight and 28 for obesity (WS/T 428-2013).
Reading the healthy weight range
The tool works backward from BMI 18.5–24.9 to give the healthy weight range (kg) for your height. If your weight is above the range, "to adjust" shows the kg to lose; below it, the kg to gain. This is a reference range, not a precise target.
Limitations of BMI
BMI does not distinguish muscle from fat or show fat distribution. Muscular athletes may have a high BMI with low body fat (healthy overweight), while some older adults have a normal BMI but low muscle mass. Combine BMI with body fat percentage and waist-to-hip ratio for the full picture.
FAQ
QWhat is the BMI formula?
Metric: BMI = weight(kg) ÷ height(m)². Imperial: BMI = weight(lb) ÷ height(in)² × 703. The tool converts units automatically.
QWhat is a normal BMI range?
WHO adult normal is 18.5–24.9; 25–29.9 is overweight and 30+ obese. Chinese adult cut-offs are stricter at 24/28.
QWhy is my BMI high but I do not look fat?
Muscle is denser than fat, so people who strength-train can land in the overweight range despite low body fat. Use body fat and waist measurements rather than BMI alone.
QDoes BMI apply to children and pregnant women?
No — this calculator uses adult standards and is not for children (who need age- and sex-specific BMI percentiles) or pregnancy. Athletes and older adults should also interpret it carefully.
QCan BMI alone tell me I am healthy?
No. It ignores fat distribution and composition, so pair it with body fat percentage and waist-to-hip ratio — even "normal-weight obesity" carries metabolic risk.