BMI Calculator
Find your Body Mass Index and see which weight category you fall into.
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📘 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.
💡 Expert Tips
BMI 18.5–24.9 is the normal range for most adults.
Athletes may score high from muscle, not fat.
Asian adults face higher health risk above BMI 23.
Pair BMI with waist measurement for a fuller picture.
How to read your result
A single BMI reading is a snapshot, not a verdict. Under 18.5 with low energy or hair/skin changes is worth a doctor visit, not just "eat more." 18.5-24.9 with poor energy or strength can still hide a bad diet or high body fat — BMI alone won’t show that. 25-29.9 is a signal to act before it compounds, not a crisis. 30+ paired with high waist circumference is the combination that most strongly predicts real health risk — check the Waist-Hip Ratio and Body Fat calculators alongside this one before drawing conclusions.
⚠️ Common Mistakes
✕ Treating BMI as a fitness or body-composition score.
✓ BMI cannot see muscle vs fat. A muscular athlete and a sedentary person can share the same BMI with completely different health profiles — pair it with the Body Fat calculator for the fuller picture.
✕ Panicking over a single point difference (e.g. 24.9 vs 25.1).
✓ The category boundaries are population-level guidelines, not hard health cliffs. Track the trend over months, not a single day’s number — weight fluctuates 1-2kg daily from water and food alone.
✕ Using the same thresholds regardless of ethnicity.
✓ Asian populations face measurably higher health risk at lower BMI values (above 23, not 25) — if you’re of Asian descent, treat 23+ as the point to start paying attention, not 25.
⚖️ Health & Wealth — pair this with
Frequently Asked
What is a healthy BMI?▾
For most adults: under 18.5 is underweight, 18.5–24.9 is healthy, 25–29.9 is overweight, and 30+ is obese. Asian populations are generally considered at higher health risk at lower BMI values (above 23).
Is BMI always accurate?▾
No — it ignores muscle mass. Athletes can have a high BMI but be very healthy. Treat it as one screening indicator, not a definitive health measure.
How do I lower my BMI?▾
BMI decreases when you lose body fat. A calorie deficit of 500–750 calories/day typically leads to 0.5–0.75kg loss per week. Use our Calorie Calculator to find your specific target.
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Example — 175cm male
Robinson formula gives an ideal weight of approximately 68.9 kg