Is BMI a reliable indicator of health?

BMI is useful at population level and as a starting point for individual assessment, but has limits. It doesn’t distinguish muscle from fat, abdominal fat (a risk factor) from hip fat, and works poorly for children, pregnant women, elderly people and athletes. Use waist measurement or body-composition analysis (DXA/BIA) alongside for a full picture.

Are BMI thresholds different for Asian populations?

Yes. WHO recommends lower overweight thresholds for Asian populations because risk of type 2 diabetes and heart disease rises at lower BMI. Common Asian thresholds: overweight ≥ 23, obesity ≥ 25 or 27.5. The tool uses standard WHO thresholds; Asian users can read the results more strictly.

Should children use the same BMI table as adults?

No. Children and adolescents use age- and sex-specific BMI percentiles (iso-BMI or ISO-BMI). Thresholds shift with growth. Use WHO growth charts or an ISO-BMI calculator for children under 18. This calculator is calibrated for adults (≥ 18).

Should I compute BMI often?

For most people, monthly or quarterly is enough. Daily swings of ± 1 kg are mostly water and gut contents, not real fat change. Use trends over weeks, not single days, to judge whether you’re heading towards your goal.

BMI Calculator - Body Mass Index & Calorie Needs

About the calculations

BMI (body mass index) is calculated as weight divided by height squared: kg / m². It is a rough measure that does not distinguish muscle from fat, and works best for adults.

Basal metabolic rate (BMR) uses the Mifflin-St Jeor equation, and daily calorie needs are BMR multiplied by an activity factor.

The numbers are indicative and do not replace advice from a health professional.

About this tool

BMI (Body Mass Index) is a rough measure of whether your weight is healthy for your height. The formula is simple: BMI = weight (kg) / height (m)². The World Health Organization (WHO) classifies BMI values as underweight (< 18.5), normal (18.5–24.9), overweight (25–29.9) and obese (≥ 30). BMI is useful as a statistical tool and first indicator, but doesn’t capture muscle mass, fat distribution or body build, a muscular person can easily land in the "overweight" category. The calculator returns BMI, category, ideal weight range and the delta from WHO’s recommended range. Everything runs locally.

How to use it

Enter your height in centimetres (e.g. 178).
Enter your weight in kilograms (e.g. 75).
BMI is calculated instantly and shown with its category.
The tool also shows the ideal weight range for your height according to WHO.
No data is stored or sent, everything is computed locally in your browser.

Examples

Normal weight

InputHeight 178 cm, weight 72 kg

OutputBMI 22.7, Normal weight (WHO 18.5–24.9)

Middle of the normal-weight category. Ideal range for 178 cm: 58.6–79.0 kg.

Overweight

InputHeight 165 cm, weight 78 kg

OutputBMI 28.7, Overweight (WHO 25–29.9)

Ideal range for 165 cm: 50.4–67.8 kg. Getting below 68 kg gives BMI < 25.

Heavily muscular

InputHeight 185 cm, weight 105 kg (bodybuilder)

OutputBMI 30.7, Obesity class 1 (WHO)

Classic "BMI paradox". Muscle weighs more than fat, use body composition analysis or fat measurement for a real assessment.

Common use cases

Quick check whether weight falls within the WHO recommended range.
Setting weight-change goals using the ideal-weight range as reference.
GPs and other healthcare use BMI as an initial screening tool.
Comparing before/after in a weight-loss programme (enter height once, update weight).
Estimating risk of chronic diseases linked to underweight/obesity (as part of multiple measures).
Comparing population BMI across countries and age groups (epidemiology).

Frequently asked questions

Is BMI a reliable indicator of health?: BMI is useful at population level and as a starting point for individual assessment, but has limits. It doesn’t distinguish muscle from fat, abdominal fat (a risk factor) from hip fat, and works poorly for children, pregnant women, elderly people and athletes. Use waist measurement or body-composition analysis (DXA/BIA) alongside for a full picture.
Are BMI thresholds different for Asian populations?: Yes. WHO recommends lower overweight thresholds for Asian populations because risk of type 2 diabetes and heart disease rises at lower BMI. Common Asian thresholds: overweight ≥ 23, obesity ≥ 25 or 27.5. The tool uses standard WHO thresholds; Asian users can read the results more strictly.
Should children use the same BMI table as adults?: No. Children and adolescents use age- and sex-specific BMI percentiles (iso-BMI or ISO-BMI). Thresholds shift with growth. Use WHO growth charts or an ISO-BMI calculator for children under 18. This calculator is calibrated for adults (≥ 18).
Should I compute BMI often?: For most people, monthly or quarterly is enough. Daily swings of ± 1 kg are mostly water and gut contents, not real fat change. Use trends over weeks, not single days, to judge whether you’re heading towards your goal.

Technical background

The formula BMI = kg / m² was developed by Belgian statistician Adolphe Quetelet in the 1830s and was originally called the "Quetelet Index". The term "Body Mass Index" was coined by Ancel Keys in 1972. WHO adopted the categories used today: underweight (< 18.5), normal (18.5–24.9), overweight (25–29.9), obese class 1 (30–34.9), class 2 (35–39.9), class 3 (≥ 40). The ideal weight range for a given height is BMI_min × height² and BMI_max × height². Alternative measures: waist-to-height ratio (WHtR, target < 0.5), body fat percentage (DXA scan), BAI (Body Adiposity Index), FMI (Fat Mass Index). No single index captures full health status, several measures together give a better picture.

Underweight	< 18,5
Normal	18,5, 24,9
Overweight	25,0, 29,9
Obese	≥ 30,0

BMI categories (adults)