BMI Calculator
Use this BMI calculator to calculate your body mass index and see where your weight falls on the standard BMI scale.
Calculated instantly in your browser — nothing is sent to or stored on our servers.
Kevin Cyr, MD
Kevin Cyr, MD, is a board-certified internal medicine physician who trained at Stanford University School of Medicine and completed residency at Cedars-Sinai Medical Center.
Medical Disclaimer: This calculator provides a general estimate based on established research and is for educational purposes only, not a substitute for medical advice. Individual results can vary based on health conditions, so consult a qualified healthcare professional or registered dietitian before making significant changes to your diet, exercise, or health routine. Read our full Medical Disclaimer.
How Body Mass Index (BMI) Is Calculated
BMI, or Body Mass Index, is a number calculated from your height and weight that places you into a general weight category linked to health risk. It's the same basic measurement used in doctor's offices, public health research, and international health guidelines. Here's exactly how it's calculated and how to read your result.
What BMI Measures
BMI is a screening tool, not a body composition test. It does not measure body fat directly, and it cannot tell the difference between fat and muscle.
The Formula
For users working in metric units:
BMI = weight in kilograms ÷ (height in meters)²
For users working in imperial units:
BMI = [weight in pounds ÷ (height in inches)²] × 703
The 703 in the imperial formula converts pounds and inches into the same units the metric formula produces, so your BMI comes out the same either way. The formula itself dates back to the 1830s, and researcher Ancel Keys confirmed in 1972 that it remains one of the most reliable simple screening ratios available¹.
How This Calculator Computes Your Result
Enter your height and weight in either imperial or metric units using the toggle above. We convert everything to a common unit behind the scenes, apply the formula, and round your result to one decimal place before matching it to a category.
What Your Result Means
BMI (kg/m²) | Category |
Below 18.5 | Underweight |
18.5 to 24.9 | Healthy Weight |
25.0 to 29.9 | Overweight |
30.0 and above | Obese |
These cutoffs come from the CDC² and the National Heart, Lung, and Blood Institute³, and have been the U.S. clinical standard since 1998³.
Why the Cutoffs Differ for Some Populations
These ranges were built mostly from European and North American data. A WHO review found that several Asian populations face higher health risk at lower BMI levels than the standard cutoff of 25⁴. Because of this, the WHO added extra reference points for those populations rather than replacing the global standard⁴.
A Note on Accuracy
BMI cannot tell fat from muscle. A very muscular person may score as overweight despite low body fat, while someone with little muscle may score as healthy despite carrying more fat than the number suggests. Treat your BMI as a starting point, and pair it with a waist measurement or body fat estimate for a fuller picture.
Frequently Asked Questions
What is a healthy BMI?
A BMI between 18.5 and 24.9 falls in the healthy weight range for most adults². Below 18.5 is considered underweight, and 25 or above is considered overweight or obese.
Is BMI accurate, or does it miss things like muscle mass?
It misses body composition entirely. BMI cannot measure fat directly, and a widely cited clinical review documents it as an imperfect stand-in for actual body fat percentage⁵. A muscular person can score as overweight without carrying excess fat.
Do BMI categories apply the same way to everyone?
Not quite. Some Asian populations face higher health risk at lower BMI levels than the standard cutoff⁴. The WHO added extra reference points for those groups rather than replacing the global categories.
How often should I recalculate my BMI?
After a noticeable weight change, or about once a year at a routine checkup. Small day-to-day weight shifts rarely move you into a new category.
Sources
Indices of Relative Weight and Obesity, Keys et al., 1972
Adult BMI Categories, CDC
The Practical Guide: Identification, Evaluation, and Treatment of Overweight and Obesity in Adults, NHLBI
Appropriate Body-Mass Index for Asian Populations, WHO Expert Consultation, 2004
Body Mass Index: Obesity, BMI, and Health: A Critical Review, Nuttall, 2015
BMI Calculator
Use this BMI calculator to calculate your body mass index and see where your weight falls on the standard BMI scale.
Calculated instantly in your browser — nothing is sent to or stored on our servers.
Kevin Cyr, MD
Kevin Cyr, MD, is a board-certified internal medicine physician who trained at Stanford University School of Medicine and completed residency at Cedars-Sinai Medical Center.
Medical Disclaimer: This calculator provides a general estimate based on established research and is for educational purposes only, not a substitute for medical advice. Individual results can vary based on health conditions, so consult a qualified healthcare professional or registered dietitian before making significant changes to your diet, exercise, or health routine. Read our full Medical Disclaimer.
How Body Mass Index (BMI) Is Calculated
BMI, or Body Mass Index, is a number calculated from your height and weight that places you into a general weight category linked to health risk. It's the same basic measurement used in doctor's offices, public health research, and international health guidelines. Here's exactly how it's calculated and how to read your result.
What BMI Measures
BMI is a screening tool, not a body composition test. It does not measure body fat directly, and it cannot tell the difference between fat and muscle.
The Formula
For users working in metric units:
BMI = weight in kilograms ÷ (height in meters)²
For users working in imperial units:
BMI = [weight in pounds ÷ (height in inches)²] × 703
The 703 in the imperial formula converts pounds and inches into the same units the metric formula produces, so your BMI comes out the same either way. The formula itself dates back to the 1830s, and researcher Ancel Keys confirmed in 1972 that it remains one of the most reliable simple screening ratios available¹.
How This Calculator Computes Your Result
Enter your height and weight in either imperial or metric units using the toggle above. We convert everything to a common unit behind the scenes, apply the formula, and round your result to one decimal place before matching it to a category.
What Your Result Means
BMI (kg/m²) | Category |
Below 18.5 | Underweight |
18.5 to 24.9 | Healthy Weight |
25.0 to 29.9 | Overweight |
30.0 and above | Obese |
These cutoffs come from the CDC² and the National Heart, Lung, and Blood Institute³, and have been the U.S. clinical standard since 1998³.
Why the Cutoffs Differ for Some Populations
These ranges were built mostly from European and North American data. A WHO review found that several Asian populations face higher health risk at lower BMI levels than the standard cutoff of 25⁴. Because of this, the WHO added extra reference points for those populations rather than replacing the global standard⁴.
A Note on Accuracy
BMI cannot tell fat from muscle. A very muscular person may score as overweight despite low body fat, while someone with little muscle may score as healthy despite carrying more fat than the number suggests. Treat your BMI as a starting point, and pair it with a waist measurement or body fat estimate for a fuller picture.
Frequently Asked Questions
What is a healthy BMI?
A BMI between 18.5 and 24.9 falls in the healthy weight range for most adults². Below 18.5 is considered underweight, and 25 or above is considered overweight or obese.
Is BMI accurate, or does it miss things like muscle mass?
It misses body composition entirely. BMI cannot measure fat directly, and a widely cited clinical review documents it as an imperfect stand-in for actual body fat percentage⁵. A muscular person can score as overweight without carrying excess fat.
Do BMI categories apply the same way to everyone?
Not quite. Some Asian populations face higher health risk at lower BMI levels than the standard cutoff⁴. The WHO added extra reference points for those groups rather than replacing the global categories.
How often should I recalculate my BMI?
After a noticeable weight change, or about once a year at a routine checkup. Small day-to-day weight shifts rarely move you into a new category.
Sources
Indices of Relative Weight and Obesity, Keys et al., 1972
Adult BMI Categories, CDC
The Practical Guide: Identification, Evaluation, and Treatment of Overweight and Obesity in Adults, NHLBI
Appropriate Body-Mass Index for Asian Populations, WHO Expert Consultation, 2004
Body Mass Index: Obesity, BMI, and Health: A Critical Review, Nuttall, 2015
BMI Calculator
Use this BMI calculator to calculate your body mass index and see where your weight falls on the standard BMI scale.
Calculated instantly in your browser — nothing is sent to or stored on our servers.
Kevin Cyr, MD
Kevin Cyr, MD, is a board-certified internal medicine physician who trained at Stanford University School of Medicine and completed residency at Cedars-Sinai Medical Center.
Medical Disclaimer: This calculator provides a general estimate based on established research and is for educational purposes only, not a substitute for medical advice. Individual results can vary based on health conditions, so consult a qualified healthcare professional or registered dietitian before making significant changes to your diet, exercise, or health routine. Read our full Medical Disclaimer.
How Body Mass Index (BMI) Is Calculated
BMI, or Body Mass Index, is a number calculated from your height and weight that places you into a general weight category linked to health risk. It's the same basic measurement used in doctor's offices, public health research, and international health guidelines. Here's exactly how it's calculated and how to read your result.
What BMI Measures
BMI is a screening tool, not a body composition test. It does not measure body fat directly, and it cannot tell the difference between fat and muscle.
The Formula
For users working in metric units:
BMI = weight in kilograms ÷ (height in meters)²
For users working in imperial units:
BMI = [weight in pounds ÷ (height in inches)²] × 703
The 703 in the imperial formula converts pounds and inches into the same units the metric formula produces, so your BMI comes out the same either way. The formula itself dates back to the 1830s, and researcher Ancel Keys confirmed in 1972 that it remains one of the most reliable simple screening ratios available¹.
How This Calculator Computes Your Result
Enter your height and weight in either imperial or metric units using the toggle above. We convert everything to a common unit behind the scenes, apply the formula, and round your result to one decimal place before matching it to a category.
What Your Result Means
BMI (kg/m²) | Category |
Below 18.5 | Underweight |
18.5 to 24.9 | Healthy Weight |
25.0 to 29.9 | Overweight |
30.0 and above | Obese |
These cutoffs come from the CDC² and the National Heart, Lung, and Blood Institute³, and have been the U.S. clinical standard since 1998³.
Why the Cutoffs Differ for Some Populations
These ranges were built mostly from European and North American data. A WHO review found that several Asian populations face higher health risk at lower BMI levels than the standard cutoff of 25⁴. Because of this, the WHO added extra reference points for those populations rather than replacing the global standard⁴.
A Note on Accuracy
BMI cannot tell fat from muscle. A very muscular person may score as overweight despite low body fat, while someone with little muscle may score as healthy despite carrying more fat than the number suggests. Treat your BMI as a starting point, and pair it with a waist measurement or body fat estimate for a fuller picture.
Frequently Asked Questions
What is a healthy BMI?
A BMI between 18.5 and 24.9 falls in the healthy weight range for most adults². Below 18.5 is considered underweight, and 25 or above is considered overweight or obese.
Is BMI accurate, or does it miss things like muscle mass?
It misses body composition entirely. BMI cannot measure fat directly, and a widely cited clinical review documents it as an imperfect stand-in for actual body fat percentage⁵. A muscular person can score as overweight without carrying excess fat.
Do BMI categories apply the same way to everyone?
Not quite. Some Asian populations face higher health risk at lower BMI levels than the standard cutoff⁴. The WHO added extra reference points for those groups rather than replacing the global categories.
How often should I recalculate my BMI?
After a noticeable weight change, or about once a year at a routine checkup. Small day-to-day weight shifts rarely move you into a new category.
Sources
Indices of Relative Weight and Obesity, Keys et al., 1972
Adult BMI Categories, CDC
The Practical Guide: Identification, Evaluation, and Treatment of Overweight and Obesity in Adults, NHLBI
Appropriate Body-Mass Index for Asian Populations, WHO Expert Consultation, 2004
Body Mass Index: Obesity, BMI, and Health: A Critical Review, Nuttall, 2015