BMI Calculator — Check Your Body Mass Index Free (kg/cm & lbs/ft)

Body Mass Index (BMI) is the most widely used screening tool to check if your weight is healthy for your height. Whether you are starting a fitness journey, tracking health goals, or just curious about your numbers, our free BMI calculator gives you instant results with zero signup. Unlike basic calculators that only show a number, this tool explains what your BMI means, shows your healthy weight range, and breaks down the exact formula — so you understand the math, not just the result. It works with both metric (kg/cm) and imperial (lbs/ft+in) units, making it usable no matter where you live.

Metric: enter height in centimetres (e.g. 170).

How to Use the BMI Calculator

Using this tool takes less than 10 seconds. Here is exactly what to do:

  1. Select your units — Choose kg/cm or lbs/ft+in from the toggle buttons.
  2. Enter your weight — Type your current body weight.
  3. Enter your height — For metric, enter height in cm. For imperial, enter feet and inches separately.
  4. Click Calculate — Your BMI number, category, and healthy weight range appear instantly.

Example: If you weigh 70 kg and your height is 175 cm, your BMI is 22.9 — which falls in the normal weight category. Your healthy weight range for this height is approximately 56.7 kg to 76.6 kg.

All calculations run privately in your browser — no data is sent to any server.

What Is BMI and Why Does It Matter?

BMI stands for Body Mass Index. It is a simple mathematical ratio developed in the 1830s by Belgian mathematician Adolphe Quetelet and later adopted by the World Health Organization (WHO) as a population-level health screening tool.

Your BMI places you into one of four main categories:

BMI RangeCategory
Below 18.5Underweight
18.5 – 24.9Normal weight
25.0 – 29.9Overweight
30.0 and aboveObese

Doctors and health organizations use BMI as a first-line screening tool because it is fast, non-invasive, and requires no special equipment. It helps identify individuals who may be at higher risk for conditions like type 2 diabetes, heart disease, high blood pressure, and certain cancers.

However, BMI is not a diagnostic tool. It does not measure body fat directly, nor does it account for muscle mass, bone density, age, or fat distribution. A bodybuilder and a sedentary person can have the same BMI but completely different body compositions. That is why BMI should always be considered alongside other health markers.

The BMI Formula Explained with Real Examples

Understanding the formula helps you verify results and calculate BMI manually when needed.

The standard BMI formula (metric):

BMI = weight (kg) ÷ [height (m) × height (m)]

Step-by-step example:

  • Weight = 70 kg
  • Height = 175 cm = 1.75 m
  • BMI = 70 ÷ (1.75 × 1.75)
  • BMI = 70 ÷ 3.0625
  • BMI = 22.9

The imperial formula:

BMI = 703 × weight (lbs) ÷ [height (inches) × height (inches)]

Step-by-step example:

  • Weight = 154 lbs
  • Height = 5 feet 9 inches = 69 inches
  • BMI = 703 × 154 ÷ (69 × 69)
  • BMI = 108,262 ÷ 4,761
  • BMI = 22.7 (slight rounding difference from metric)

Quick reference table for common heights:

Height Healthy Weight Range (kg) Healthy Weight Range (lbs)
160 cm (5'3")47.4 – 63.8104 – 141
165 cm (5'5")50.4 – 67.8111 – 149
170 cm (5'7")53.5 – 72.1118 – 159
175 cm (5'9")56.7 – 76.6125 – 169
180 cm (5'11")60.0 – 81.0132 – 178
185 cm (6'1")63.4 – 85.6140 – 189

Important Limitations & Common Mistakes

Do not make these mistakes when using BMI:

  • Ignoring muscle mass: Athletes and bodybuilders often have BMIs in the "overweight" or "obese" range due to high muscle density. If you train regularly, consider using our Body Fat Calculator for a more accurate picture.
  • Using adult cutoffs for children: BMI categories for kids and teens are interpreted using age and gender-specific percentiles. Adult BMI cutoffs do not apply.
  • Forgetting waist circumference: Where you carry fat matters. Abdominal fat (visceral fat) is more dangerous than fat stored in the hips or thighs.
  • Treating BMI as a diagnosis: BMI is a screening number, not a medical diagnosis. Always consult a healthcare provider for personalized advice.

Frequently Asked Questions

How do I calculate BMI manually?
Use the formula: weight in kg divided by height in meters squared. For example, 70 kg and 1.75 m gives 70 ÷ (1.75 × 1.75) = 22.9.
What is a healthy BMI for men and women?
For most adults, a BMI between 18.5 and 24.9 is considered normal. The ranges are the same for men and women, though body composition differs.
Can I use this BMI calculator for kids?
Adult BMI categories do not apply to children. Pediatricians use BMI-for-age percentiles. Use this calculator only as a rough guide for teens and consult a doctor.
Is BMI accurate for athletes?
No. Because muscle weighs more than fat, muscular individuals often have higher BMIs despite low body fat. Use a body fat percentage test for accuracy.
What is the BMI formula for pounds and inches?
BMI = 703 × weight (lbs) ÷ [height (inches)]². For example, 154 lbs and 69 inches gives approximately 22.7.
Why did my BMI change if my weight is the same?
If you updated your height measurement or switched units incorrectly, the result changes. Double-check your inputs — especially converting cm to feet/inches.
What BMI is considered obese?
A BMI of 30.0 or higher falls into the obese category. This is further divided into Class 1 (30–34.9), Class 2 (35–39.9), and Class 3 (40+).
Can BMI tell me how much weight I need to lose?
Not directly, but you can use the healthy weight range shown in our calculator to set a target. For personalized plans, consult a nutritionist.
Is this BMI calculator free to use?
Yes. SnapCalc's BMI calculator is 100% free, requires no signup, and runs entirely in your browser for privacy.
What is a better alternative to BMI?
For a more complete picture, combine BMI with body fat percentage, waist-to-hip ratio, and fitness assessments. Try our Body Fat Calculator or Calorie & Macro Calculator.

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