Does normal BMI depend on age?
No for adults, the range of normal BMI is 18.5-24.9, and it does not depend on a person's age. For children, however, age is essential in assessing their weight.
BMI Calculator
Body Mass Index
24.2 Normal weight
BMI Prime: 0.97
24.2
<18.5
18.5-25
25-30
>30
Underweight
Normal weight
Overweight
Obese
BMI Calculator – Calculate Your Body Mass Index
What is BMI Calculator?
Understanding Body Mass Index
Our free online BMI calculator is a useful tool that measures whether you are overweight, underweight, or just right. Your weight alone is not enough to tell, as a tall, skinny man may easily weigh more than a short but rotund woman. The body mass index calculator, or BMI calculator, overcomes this problem by finding a ratio of your weight to your height and returning a single number.
This number will fit into a category on the scale of BMI ranges, which are defined as underweight, normal, overweight, and obese. Use our BMI calculator online to get instant results and understand what your BMI number means.
Why BMI Matters
To work out your body mass index on your own and what the number means for you, you'll need to know the following:
- How to calculate BMI - Learn more about the BMI formula
- What is a normal BMI? - Discover healthy BMI ranges
- What the various BMI ranges are - View the complete BMI chart
Important: BMI is a screening tool, not a diagnostic tool. It doesn't account for muscle mass, bone density, body composition, or other health factors. This calculator provides educational information only and is not a substitute for professional medical advice. For personalized health guidance, consult with a healthcare professional.
BMI is used as a screening tool for both individual health assessment and population health studies. According to the CDC, BMI helps identify potential weight-related health risks at both the individual and community levels. For individual use, BMI provides a quick assessment of weight status. For population health, BMI data helps track trends and inform public health policies.
How do I calculate BMI?
BMI Formula
To compute BMI, you need to: For a detailed explanation, see our BMI formula guide.
- Divide your weight (in kilograms) by your height (in meters).
- Divide the answer by your height again to get your BMI.
- That is the body mass index formula. Expressed differently, it is:
BMI = weight / height²Step-by-Step Calculation
Here's a detailed example: If you weigh 70 kg and are 1.75 m tall:
BMI = 70 / (1.75)² = 70 / 3.06 = 22.9Example Calculations
This formula gives you a single number that categorizes your weight status according to standard BMI ranges. You can use our free online BMI calculator above to get instant results without manual calculations. Our BMI calculator supports both metric and imperial units, making it easy to calculate BMI regardless of your preferred measurement system.
How to Measure Height and Weight Accurately
Accurate measurements are essential for reliable BMI calculations. According to the CDC, following proper measurement techniques ensures you get the most accurate results:
Measuring Height:
- Stand straight against a wall with your heels, back, and head touching the wall
- Look straight ahead, keeping your eyes level with the floor
- Use a flat object (like a book) to mark the top of your head on the wall
- Measure from the floor to the mark using a measuring tape
- Measure in the morning for the most accurate height (you may be slightly shorter later in the day)
Measuring Weight:
- Use a reliable, calibrated scale on a hard, flat surface
- Weigh yourself at the same time of day (preferably in the morning, after using the bathroom)
- Wear minimal clothing (or the same amount of clothing each time)
- Stand still on the scale with your weight evenly distributed
- Take multiple measurements and use the average for the most accurate result
For children and teens, accurate measurements are especially important. Healthcare providers use growth charts that require precise height and weight measurements. Always measure children using the same scale and measuring technique for consistency.
Normal BMI
Our BMI calculator makes it a piece of cake for you to find your number. However, please remember that BMI is a rough estimation. The result can be somewhat misleading for individuals who are well-muscled (such as bodybuilders) or for those who have lost a significant amount of muscle (such as the elderly).
If you are unsure whether or not you fall within the "normal" range of muscle mass, please consider using one of our more specialized calculators. If you want to determine your body composition that adjusts for skeletal mass, you may want to use our body frame size calculator. Additionally, check out our skinfold body fat calculator to figure out what percentage of your body is fat. Learn more about maintaining healthy BMI.
A normal BMI range is typically between 18.5 and 24.9. This range is associated with the lowest risk for weight-related health problems. However, BMI is just one of many factors that determine overall health.
What are the BMI ranges?
There are five basic ranges within the BMI scale: For a visual representation, check out our interactive BMI chart.
Underweight (BMI < 18.5)
A BMI below 18.5 indicates underweight. This may suggest nutritional deficiencies or other health concerns.
Normal weight (BMI 18.5-24.9)
This is the healthy weight range associated with the lowest risk for weight-related health problems.
Overweight (BMI 25-29.9)
A BMI between 25 and 29.9 indicates overweight status, which may increase health risks. Read more about understanding and managing overweight.
Obese (BMI 30-35)
A BMI of 30-35 indicates obesity, which significantly increases the risk of various health conditions.
Severely obese (BMI 35+)
A BMI of 35 or higher indicates severe obesity, which carries very high health risks.
| BMI Range | Category | Health Risk |
|---|---|---|
| < 18.5 | Underweight | May indicate nutritional deficiencies |
| 18.5 - 24.9 | Normal weight | Lowest health risk |
| 25 - 29.9 | Overweight | Moderate health risk |
| 30 - 34.9 | Obese Class I | High health risk |
| 35+ | Severely obese | Very high health risk |
The BMI Prime is a nifty modification to our own BMI calculator. It's a decimal number where 1.0 = the upper limit to the "normal BMI" range. It's a super easy way to see if you're overweight or not. If your BMI Prime is more than 1, then you've got some weight to lose.
Using our body mass index calculator
At the top of our free online BMI calculator are fields for you to plug in your height and weight. Plug in these values, and you'll instantly have your BMI, your BMI Prime (see above), and a little message telling you what range you fall into. Our BMI calculator with results explanation helps you understand what your BMI number means for your health.
If you're overweight and want to know exactly how much you'll have to lose to get into the healthy range, you can do that too. Leave your height and weight in the boxes where they are, and type "0.9" into the BMI Prime box. Your weight and BMI will adjust themselves. Explore our BMI for men and BMI for women guides for gender-specific considerations.
💡 Tip
If your height box adjusts itself when you change other boxes, you'll need to lock it. Click the right-hand panel of the box and select the lock icon to hold that figure in place while you play with the values in other boxes. That is... unless you plan on growing taller!
Other considerations
If you want to know if your metabolism is on your side in your quest towards a healthy weight, try our basal metabolic rate calculator. We often hear about things raising or lowering our metabolism (which one does skipping breakfast do again?), but we don't hear much about tracking those changes. That's what this calculator is for.
Your basal metabolic rate is the activity level of your body's metabolism when you wake up in the morning. This is the most reliable time of the day to measure metabolism since the day hasn't had time to heat you up yet! For children, use our BMI calculator for children, and for athletes, check our BMI guide for athletes.
Once you know how to calculate BMI, the next logical figure to know is your ideal weight. Use our ideal weight calculator to figure this out in a jiffy. You can also use our maintenance calorie calculator to calculate how many calories your body needs to maintain your current weight.
Frequently Asked Questions (FAQs)
What is my BMI if I am a man and weigh 75 kilos?
The answer depends on your height! Assume it is 180 cm. Then your BMI is:
BMI = weight / height²where the weight should be in kg and height should be in meters.
Therefore, convert height in cm to meters: 180/100 = 1.8 m.
So the BMI calculation is weight / height² = 75/1.8² = 23.148. So, it is in the normal (healthy) range. Note that this result does not depend on your gender!
What is a healthy BMI?
A healthy BMI for adults is typically between 18.5 and 24.9. This range is associated with the lowest risk for weight-related health problems. However, BMI should be considered alongside other health indicators such as waist circumference, body composition, and overall health status.
Is BMI accurate for athletes?
BMI may not be accurate for athletes or individuals with high muscle mass, as muscle weighs more than fat. Athletes may have a higher BMI despite being in excellent health. In such cases, other measurements like body fat percentage or waist-to-hip ratio may provide more accurate assessments.
Medical Disclaimer
Important: BMI is a screening tool, not a diagnostic tool. It provides an estimate of body fat based on height and weight but does not directly measure body fat percentage, muscle mass, bone density, or overall health.
BMI should not be used as the sole indicator of health. Many factors influence health beyond BMI, including:
- Body composition (muscle vs. fat)
- Waist circumference and body fat distribution
- Physical fitness and activity levels
- Medical history and family history
- Blood pressure, cholesterol, and blood sugar levels
- Lifestyle factors (diet, exercise, sleep, stress)
This calculator provides educational information only and is not a substitute for professional medical advice, diagnosis, or treatment. Always consult with a qualified healthcare provider for personalized health guidance, especially if you have concerns about your weight or health status.