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BMI Calculator

Find your Body Mass Index and see which weight category you fall into.

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Ideal Weight Calculator

Example — 175cm male

Robinson formula gives an ideal weight of approximately 68.9 kg

Open Ideal Weight →

📘 What is the BMI Calculator?

Body Mass Index (BMI) is a quick screening number that compares your weight to your height. Doctors, insurers and fitness apps all use it as a first checkpoint — not because it is perfect, but because it is fast, free, and correlates reasonably well with health risk across large populations. This calculator gives you your exact BMI instantly, tells you which official category you fall into, and shows the healthy weight range for your height so you know exactly how many kilograms separate you from the normal range.

⚙️ How BMI is calculated

The BMI formula

BMI is calculated as weight in kilograms divided by height in metres squared (BMI = kg ÷ m²). For imperial units, the formula becomes weight in pounds × 703, divided by height in inches squared. This calculator handles both unit systems automatically — just toggle between metric and imperial and the conversion happens instantly.

Why height is squared

Body weight tends to scale with the square of height because volume (and therefore mass) scales roughly with the square of a linear dimension for similarly-shaped bodies. Squaring height in the denominator removes most of the natural size advantage that taller people would otherwise have, making BMI a fairer comparison across different heights.

The five BMI categories

The World Health Organization defines five bands: under 18.5 is underweight, 18.5–24.9 is normal weight, 25–29.9 is overweight, 30–34.9 is Obese Class I, and 35 and above is Obese Class II or higher. Each band carries a different general health-risk profile, which this calculator highlights with colour-coded results.

BMI formula (metric)

BMI = weight (kg) ÷ height (m)²

Imperial: BMI = weight (lb) × 703 ÷ height (in)²

🧮 Worked examples

Example 1 — Metric

A person weighing 70 kg with a height of 175 cm (1.75 m).

→ BMI = 70 ÷ (1.75 × 1.75) = 70 ÷ 3.0625 ≈ 22.9 — Normal weight

Example 2 — Imperial

A person weighing 180 lbs with a height of 5 ft 10 in (70 inches).

→ BMI = 180 × 703 ÷ (70 × 70) = 126,540 ÷ 4,900 ≈ 25.8 — Overweight

Example 3 — Healthy range for a fixed height

For someone 165 cm tall, the normal BMI range (18.5–24.9) maps to a weight range.

→ Healthy weight ≈ 50.4 kg to 67.8 kg for 165 cm height

💡 Original insights & how to use this calculator

Tracking progress during a weight-loss programme

BMI is most useful as a trend, not a single snapshot. Recalculating it every 2–4 weeks during a weight-loss programme shows whether your changes in diet and exercise are moving you toward the normal range — and the calculator's goal-weight section shows exactly how many kilograms remain.

A starting point before a medical check-up

Many people use this calculator before a doctor visit to understand where they stand. While your doctor will look at additional factors (waist circumference, blood pressure, family history), arriving with your BMI already calculated makes that conversation more productive.

Why athletes and very muscular people should look beyond BMI

Because BMI cannot distinguish muscle from fat, a muscular athlete can show a BMI in the "overweight" band while having very low body fat. If your BMI seems high but you train regularly, pair this result with our Body Fat Percentage Calculator for a more complete picture.

BMI and health risk in Asian populations

Research shows that health risks linked to excess weight begin at lower BMI values for many Asian populations. Some health bodies recommend using 23 (rather than 25) as the overweight threshold for these groups — keep this in mind when interpreting borderline results.