What is BMI and why is it important?

Body Mass Index (BMI) is a measure of body fat based on height and weight. It's calculated as: BMI = (weight in pounds / (height in inches)^2) * 703. BMI is important because it helps identify weight categories and health risks associated with being underweight, normal weight, overweight, or obese.

What does the BMI calculator measure?

Our calculator measures: BMI (Body Mass Index), body fat percentage using the US Navy formula, ideal body weight based on a BMI of 22, body fat mass in pounds, lean body mass (muscle and bone weight), and how much weight you need to lose or gain to reach your ideal weight.

What is body fat percentage and how is it calculated?

Body fat percentage is the proportion of your total weight that is fat. This calculator uses the US Navy formula which uses neck and waist circumference (and hip circumference for females) along with height to estimate body fat percentage. For males: BF% = 495 / (1.0324 - 0.19077 * log10(waist - neck) + 0.15456 * log10(height)) - 450

What are healthy BMI ranges?

Healthy BMI ranges are: Underweight ( = 30.0). For adults, a BMI between 18.5 and 24.9 is considered normal weight.

What are healthy body fat percentage ranges?

For males: Essential Fat (2-5%), Athletes (6-13%), Fitness (14-17%), Average (18-24%), Obese (25%+). For females: Essential Fat (10-13%), Athletes (14-20%), Fitness (21-24%), Average (25-31%), Obese (32%+). These ranges vary based on age and individual factors.

How accurate is this BMI and body fat calculator?

BMI calculations are quite accurate, but body fat percentage estimates using circumference measurements (Navy formula) are estimates typically accurate within 3-4%. For more precise body fat measurements, consider DEXA scans, hydrostatic weighing, or professional bioelectrical impedance analysis.

How should I measure my neck and waist circumference?

Neck: Measure just below the larynx (Adam's apple) with your head in a normal position, not tilted. Waist: Measure at navel level while standing relaxed. Hip (females only): Measure at the widest point of your hips. Use a flexible measuring tape and keep it snug but not tight.

Can BMI be misleading?

Yes, BMI has limitations. It doesn't distinguish between muscle and fat, so very muscular individuals may have a high BMI despite being healthy. It also doesn't account for age, bone density, or body composition. For these reasons, combining BMI with body fat percentage provides a more complete picture of health.

What is an ideal body weight?

This calculator estimates ideal body weight based on a BMI of 22, which falls in the normal weight range. However, ideal weight varies by individual factors including age, gender, muscle mass, bone structure, and personal health goals. Consult with a healthcare provider for a personalized ideal weight target.

BMI & Body Fat Calculator

Calculate your Body Mass Index (BMI) and estimate your body fat percentage

Your Measurements

Gender

Male Female

Age (years)

Height

ft in

Weight (lbs)

Neck Circumference (inches) Measured just below the larynx

Waist Circumference (inches) Measured at navel level

Your Body Composition

BMI (Body Mass Index)

25.8

Overweight

Body Fat %

7.1%

Fitness

Ideal Body Weight

70lbs

Based on BMI 22

Body Fat Mass

13lbs

Total fat weight

Lean Body Mass

167lbs

Muscle and bone weight

Weight to Goal

110lbs

to lose

Summary: Your BMI is 25.8 (Overweight), and your estimated body fat percentage is 7.1% (Fitness). Your lean body mass is 167 lbs.

BMI Categories (kg/m²)

Underweight

< 18.5

Normal

18.5-24.9

Overweight

25.0-29.9

Obese

>= 30.0

Body Fat Percentage Categories

Based on age and gender standards:

Male Categories

Essential Fat: 2-5%
Athletes: 6-13%
Fitness: 14-17%
Average: 18-24%
Obese: 25%+

Measurement Tips

Neck: Just below larynx
Waist: At navel level
Use flexible measuring tape
Measure in same spot each time

Related Tools

Explore these additional calculators to optimize your health and fitness:

Calorie Calculator TDEE Calculator Weight Loss Timeline

Understanding BMI and Body Fat Percentage

What This Calculator Does

This BMI and Body Fat Calculator provides a comprehensive analysis of your body composition using your personal measurements. It calculates five key metrics:

BMI (Body Mass Index) - A measure of body weight relative to height
Body Fat Percentage - The proportion of your weight that is fat tissue
Body Fat Mass - The actual weight of all fat tissue
Lean Body Mass - Your muscle, bone, and other non-fat tissue weight
Ideal Body Weight - A target weight based on healthy BMI standards

How the Formulas Work

BMI Formula

BMI is calculated using a simple formula based on height and weight:

BMI = (weight in pounds / (height in inches)²) × 703

This formula gives you a number that helps classify your weight status. While BMI is useful for population-level assessments, it doesn't distinguish between muscle and fat, so athletes or very muscular individuals may have a high BMI despite being healthy.

Body Fat Percentage Formula (US Navy Method)

This calculator uses the US Navy formula, which is more accurate than BMI alone because it accounts for body composition:

For Males:

BF% = 495 / (1.0324 - 0.19077 × log??(waist - neck) + 0.15456 × log??(height)) - 450

For Females:

BF% = 495 / (1.29579 - 0.35004 × log??(waist + hip - neck) + 0.22100 × log??(height)) - 450

The Navy formula uses circumference measurements because fat distribution differs between body regions. Typical accuracy is within 3-4% of actual body fat when measured correctly.

Example Calculations

Example 1: Male, 180 lbs, 5'10"

Measurements:

Height: 5'10" (70 inches)
Weight: 180 lbs
Neck: 15.5 inches
Waist: 33 inches

Results:

BMI = (180 / (70²)) × 703 = 25.8 (Overweight)
Body Fat % = 18.5% (Average)
Body Fat Mass = 33.3 lbs
Lean Body Mass = 146.7 lbs
Ideal Body Weight = 171 lbs

Example 2: Female, 150 lbs, 5'5"

Measurements:

Height: 5'5" (65 inches)
Weight: 150 lbs
Neck: 13 inches
Waist: 28 inches
Hip: 36 inches

Results:

BMI = (150 / (65²)) × 703 = 24.9 (Normal Weight)
Body Fat % = 22.1% (Fitness)
Body Fat Mass = 33.2 lbs
Lean Body Mass = 116.8 lbs
Ideal Body Weight = 148 lbs

How to Use This Calculator

Step 1: Select Your Gender

Choose whether you are male or female. This is important because body fat percentage categories and formulas differ between genders.

Step 2: Enter Your Age and Basic Measurements

Input your age, height (in feet and inches), and current weight in pounds. These measurements are used for the BMI calculation.

Step 3: Measure Your Body Circumferences

Measurement Tips:

Neck Circumference: Measure just below your larynx (Adam's apple) with your head in a normal position, not tilted down.
Waist Circumference: Measure at your navel level while standing relaxed and breathing normally. Don't suck in your stomach.
Hip Circumference (females only): Measure at the widest point of your hips/buttocks.
Use a flexible measuring tape - not a rigid ruler
Keep the tape snug but not tight - avoid compressing the skin
Measure in the same location each time for consistency

Step 4: View Your Results

Once all measurements are entered, your results will display automatically. Compare your BMI and body fat percentage to the category charts to understand where you stand health-wise.

Common Questions

Q: Is BMI alone enough to assess health?

No, BMI has limitations. It doesn't distinguish between muscle and fat, so athletes or very muscular people may have a high BMI despite being healthy. Using both BMI and body fat percentage provides a more complete picture of your body composition.

Q: How accurate is the Navy body fat formula?

The Navy formula is typically accurate within 3-4% of actual body fat percentage when measurements are taken correctly. For more precise measurements, consider professional methods like DEXA scans or hydrostatic weighing. However, for tracking progress over time, this calculator is highly consistent.

Q: What if my ideal weight seems too low?

The ideal weight is calculated based on a BMI of 22, which is in the middle of the normal range. Your personal ideal weight may vary based on muscle mass, bone structure, and individual factors. If you have significant muscle mass, a higher weight may be ideal for you. Consult with a healthcare provider for a personalized target.

Q: Should I measure myself multiple times?

Yes, it's a good idea to measure in the same location each time and take the average of multiple measurements. This helps account for minor variations in measurement technique. Measure yourself in the morning for consistency, and allow at least 2-4 weeks between measurements to see meaningful changes.

Q: What's the difference between body fat mass and lean body mass?

Body fat mass is the weight of all fat tissue. Lean body mass includes everything else: muscle, bone, organs, water, and connective tissue. Your total weight = body fat mass + lean body mass. When losing weight, the goal is usually to lose body fat while preserving or building lean body mass (through exercise and adequate protein).

Tips for Improving Your Body Composition

If You Want to Reduce Body Fat:

Create a calorie deficit (eat less than you burn)
Eat adequate protein to preserve muscle
Do both cardio and strength training
Get sufficient sleep (7-9 hours)
Stay hydrated throughout the day
Track progress weekly (weight can fluctuate daily)

If You Want to Build Muscle:

Eat slightly above your calorie maintenance
Consume adequate protein (0.8-1.0g per lb of body weight)
Do resistance training consistently
Allow time for recovery between workouts
Prioritize whole, nutrient-dense foods
Measure progress by strength gains and how clothes fit

Pro Tip: The best body composition goals are personal to you. Focus on how you feel, your energy levels, and your strength rather than just the numbers on the scale.

Quick Reference

BMI Categories:

Underweight < 18.5
Normal 18.5-24.9
Overweight 25.0-29.9
Obese ? 30.0

Body Fat % (Males):

Athletes 6-13%
Fitness 14-17%
Average 18-24%
Obese 25%+

Body Fat % (Females):

Athletes 14-20%
Fitness 21-24%
Average 25-31%
Obese 32%+

Key Formulas

BMI Formula:

(Weight lbs / Height in²) × 703

Body Composition:

Body Fat Mass = Weight × (BF% / 100)
Lean Mass = Weight - Body Fat Mass
Ideal Weight = Height² × 22 × 0.704882

Related Information

This calculator uses the US Navy body fat formula, which is one of the most accurate field methods for estimating body fat percentage.

For more accurate body fat measurement, consider professional methods like:

• DEXA scanning
• Hydrostatic weighing
• Bioelectrical impedance analysis
• Bod Pod scanning