Free BMI Calculator, Check Your BMI Online 2026

Free Health Tool

Free BMI Calculator Online: Check Your Body Mass Index in 2026

Calculate your BMI instantly with our free online BMI calculator. Supports metric (kg/cm), US imperial (lbs/ft), stones, and ounces. Get your CDC-aligned health category, ideal weight range, and personalized advice, no signup needed.

What is BMI?

BMI stands for Body Mass Index. It is a simple measurement that uses your weight and height to estimate whether you are at a healthy weight. BMI is calculated by dividing your weight in kilograms by your height in meters squared, or in the US, using pounds and inches with a conversion factor of 703.

The World Health Organization (WHO) and the Centers for Disease Control and Prevention (CDC) both use BMI as a standard screening tool to identify potential weight problems in adults. While BMI does not directly measure body fat, it is a reliable and widely-used indicator in clinical and public health settings worldwide.

BMI in the United States, Key Facts

According to the CDC, more than 42% of American adults are classified as obese (BMI 30 or above), making obesity one of the leading public health concerns in the United States. An additional 31% of US adults are classified as overweight. Understanding your BMI is the first step toward taking control of your long-term health.

The CDC recommends that all adults know their BMI and discuss it with their healthcare provider as part of routine preventive care. Our calculator uses the same formula and categories as the CDC and WHO, giving you a clinically accurate result in seconds.

💡 Quick fact: In the US, BMI is most commonly calculated using pounds and inches. Use the Imperial (lbs/ft) or Stones option in the calculator above for an instant result without any manual conversion.

BMI Categories, What Your Number Means

Once you calculate your BMI, your result falls into one of these categories defined by the WHO and CDC:

BMI Range	Category	Health Risk
Below 18.5	Underweight	Moderate risk - nutritional deficiency
18.5 - 24.9	Normal weight	Low risk - healthy range
25.0 - 29.9	Overweight	Increased risk - lifestyle changes advised
30.0 - 34.9	Obese Class I	High risk - medical advice recommended
35.0 - 39.9	Obese Class II	Very high risk
40 and above	Obese Class III	Extremely high risk

How to Calculate BMI: Step by Step

You can calculate BMI manually using one of these formulas:

Metric formula: BMI = Weight (kg) ÷ [Height (m) × Height (m)]

Imperial / US formula: BMI = [Weight (lbs) ÷ Height (in)²] × 703

For example, if you weigh 154 lbs and your height is 5 ft 9 in (69 inches): BMI = [154 ÷ (69 × 69)] × 703 = [154 ÷ 4761] × 703 = 22.7 - which is in the Normal weight range.

Or simply use the free BMI calculator above - enter your weight and height in any unit (kg, lbs, oz, or stones) and get your result instantly.

BMI and Weight Units - Metric, Imperial, Stones & Ounces

Our calculator supports all common weight and height formats used around the world:

Metric (kg / cm): Standard in most countries and used by the WHO and most clinical guidelines globally.

US Imperial (lbs / ft & in): The standard in the United States. Enter your weight in pounds and height in feet and inches for an instant result.

Imperial with ounces (lbs & oz): For added precision, you can enter your weight in pounds and ounces - for example 154 lbs 8 oz - and the calculator converts automatically.

Stones (st / lbs): Commonly used in the UK and Ireland. Enter your weight in stones and pounds and the calculator handles the rest.

Limitations of BMI

BMI is a useful screening tool but it has limitations. It does not distinguish between muscle and fat, a very muscular athlete may have a high BMI but actually have very low body fat. It also does not account for age, gender, ethnicity, or where fat is distributed on your body.

Research suggests that BMI cut-offs may underestimate health risk in some ethnic groups and overestimate it in others. For a complete health assessment, always consult your doctor alongside using BMI as a guide. For authoritative BMI information, visit the CDC BMI page or the World Health Organisation website.

How to Improve Your BMI

If your BMI is outside the healthy range, small consistent lifestyle changes make a significant difference over time.

If you are overweight (BMI 25-29.9):

Start with a 30-minute daily walk, reduce sugary drinks and processed foods, and aim for a 500-calorie daily deficit through diet and exercise. Even a 5-10% reduction in body weight can meaningfully reduce your risk of type 2 diabetes, heart disease, and hypertension.

If you are underweight (BMI below 18.5):

Focus on calorie-dense nutritious foods, nuts, dairy, whole grains, lean meats, and healthy fats. Consult your doctor to rule out underlying health conditions such as thyroid disorders or nutritional deficiencies.

If you are obese (BMI 30+):

Medical guidance is strongly recommended. Read our complete guide on weight loss methods including Ozempic for medically supervised options available in the US.

Frequently Asked Questions About BMI

What is a good BMI for a woman?

For adult women, a BMI between 18.5 and 24.9 is considered healthy by the CDC and WHO. However, women naturally carry slightly more body fat than men at the same BMI, so some clinicians suggest that a BMI up to 25.5 may be acceptable depending on build and muscle mass.

What is a good BMI for a man?

For adult men, a BMI between 18.5 and 24.9 is the healthy range. Men with high muscle mass, such as athletes, may have a BMI in the overweight range (25-27) while still having very low body fat. In these cases, additional measurements like waist circumference are recommended.

Is BMI the same as body fat percentage?

No. BMI is a ratio of weight to height and does not directly measure body fat. A person with high muscle mass can have a high BMI but low body fat. For a precise body fat measurement, methods such as DEXA scan, hydrostatic weighing, or bioelectrical impedance analysis (BIA) are used.

What BMI is considered obese in the US?

In the United States, the CDC defines obesity as a BMI of 30.0 or higher in adults. This is further divided into Class I (30-34.9), Class II (35-39.9), and Class III or "severe" obesity (40+). Our calculator clearly displays which class you fall into if applicable.

Also read → Far Fewer Than 10,000 Steps a Day Can Still Provide Major Health Benefits → How to Lose Weight Fast on Ozempic: What to Expect in 2026 → How to Lose Weight Fast After Giving Birth: 12 Safe Tips

Calculate your BMI below

Free BMI Calculator

Metric · US Imperial · Stones · Ounces · WHO / CDC Standards · Instant Results

Select Gender

Weight

Height

Age (optional - for more accurate advice)

years

Please enter valid weight and height values.

Your BMI

body mass index

Healthy Range

18.5-24.9

CDC / WHO standard

Ideal Weight

for your height

⚠️BMI is a screening tool only. It does not measure body fat directly. Always consult a doctor for a complete health assessment.

💡BMI may not be accurate for athletes, pregnant women, or people over 65. Muscle weighs more than fat, so muscular people may have a higher BMI than expected.

🇺🇸In the US, over 42% of adults are classified as obese according to the CDC. Knowing your BMI is the first step toward addressing long-term health risk. Talk to your doctor about next steps.