BMI Calculator
Calculate Your Body Mass Index
Your Results
BMI Categories
BMI is a screening tool that provides a general indicator of body fat. However, it doesn’t account for muscle mass, bone density, or body composition. Athletes and individuals with high muscle mass may have a higher BMI despite being healthy. Use BMI as one tool among many for assessing health.
What is BMI and Should You Care?
Body Mass Index (BMI) is a simple calculation that uses your height and weight to estimate body fat. It’s been around since the 1800s and doctors still use it as a quick screening tool to categorize people into weight groups.
The formula divides your weight in kilograms by your height in meters squared, or if you’re working in pounds and inches, you multiply your weight by 703 and divide by your height squared.
Here’s the thing: BMI can be useful for population studies and as a rough starting point, but it’s far from perfect.
If you’re carrying significant muscle mass, which you should be – BMI can give you a completely misleading picture of your health.
BMI Categories: What the Numbers Mean
| Category | BMI Range (kg/m²) |
|---|---|
| Underweight | Below 18.5 |
| Normal Weight | 18.5 – 24.9 |
| Overweight | 25.0 – 29.9 |
| Obese Class I | 30.0 – 34.9 |
| Obese Class II | 35.0 – 39.9 |
| Obese Class III | 40.0 and above |
According to the CDC and WHO, a BMI between 18.5 and 24.9 is considered “normal weight,” 25 to 29.9 is “overweight,” and 30 or above falls into the obese categories.
These ranges are associated with different health risks, higher BMIs correlate with increased risk of heart disease, type 2 diabetes, high blood pressure, and certain cancers.
The Critical Problem: BMI Doesn’t Account for Muscle Mass
This is where BMI falls apart for anyone who lifts weights regularly. The formula treats all weight the same, it can’t distinguish between fat mass and lean muscle mass.
A 6-foot-tall guy weighing 210 pounds with 12% body fat and significant muscle mass has the same BMI (28.5, “overweight”) as a 6-foot-tall guy weighing 210 pounds with 30% body fat who hasn’t seen the inside of a gym in years.
Why BMI Fails for Muscular Individuals
Muscle is denser than fat, it takes up less space but weighs more.
If you’ve been training consistently and building muscle, your weight increases while your body fat percentage drops.
BMI interprets this as a negative because it only sees the higher number on the scale.
Research published in multiple studies shows that BMI overestimates body fat in trained individuals with high muscle mass and underestimates it in untrained individuals with low muscle mass.
Athletes, bodybuilders, and anyone who’s put in serious work in the gym can easily be misclassified as “overweight” or even “obese” despite having low body fat and excellent health markers.
LeBron James has been reported with a BMI of 26.8, technically “overweight.” Olympic sprinters often fall into the “overweight” category.
NFL running backs? Many are classified as “obese” by BMI standards. These are elite athletes in peak physical condition, yet BMI labels them as unhealthy.
Better Measures of Body Composition
If you’re serious about tracking your progress, you need better tools than BMI. Here are more accurate alternatives:
Waist Circumference: A simple tape measure around your waist tells you more about health risk than BMI. For men, a waist over 40 inches (35 inches for Asian men) indicates higher risk of metabolic disease. This measurement correlates directly with visceral fat, the dangerous fat around your organs.
Body Fat Percentage: This is what actually matters. A man at 12-18% body fat is in great shape, regardless of what BMI says. You can measure this through DEXA scans (most accurate), bioelectrical impedance scales, or skinfold calipers.
Mirror and Progress Photos: Visual assessment combined with performance metrics (strength gains, energy levels, how your clothes fit) often tells you more than any single number.
The Bottom Line:
Use BMI as one data point, but don’t obsess over it. If you’re lifting weights regularly and following a solid nutrition plan, your BMI might stay in the “overweight” range even as you lose fat and build muscle. That’s not a problem, that’s progress.
Focus on metrics that actually matter: body fat percentage, waist circumference, strength gains, and how you look and feel.
A guy with a BMI of 27 who can deadlift 400 pounds and has a 34-inch waist is infinitely healthier than a guy with a BMI of 23 who can’t do a single push-up and has a 38-inch waist.
When BMI Is Useful
BMI works reasonably well for the average sedentary population, people who don’t train regularly and have typical muscle mass.
It’s a quick, free screening tool that can flag potential health concerns. If you’re carrying significant excess fat and not training, a high BMI is a wake-up call to make changes.
For children and teens, BMI is calculated differently using age and sex-specific percentiles, and it’s generally more reliable for these populations.
What Actually Matters
Your health isn’t determined by a single number on a chart. It’s determined by your body composition, your metabolic health markers (blood pressure, cholesterol, blood sugar), your fitness level, and your overall lifestyle.
If your BMI says you’re “overweight” but you’re training hard, eating right, sleeping well, and your waist circumference and body fat percentage are in healthy ranges, you’re doing fine.
Don’t let an outdated formula from the 1800s discourage you from building muscle and getting stronger.
The reality: BMI is a screening tool designed for large populations, not a diagnostic tool for individuals, especially not for individuals who lift weights.
Use it for what it’s worth, but prioritize the metrics that actually reflect your health and progress, which are building muscle and strength. If you are looking for a plan to guide you with your training and nutrition, check out The Comeback.