Body Composition Calculator
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Bonus Tool
Weight Trend Tracker (Smoothed)
Your weight naturally fluctuates day to day due to water, food, and sodium — not just fat. Log a few entries and we'll calculate a moving average to reveal your real trend.
| Entry # | Weight (kg) | Moving Average | Trend |
|---|---|---|---|
| Add at least 3 entries to see your smoothed trend. | |||
3-Entry Moving Average Trend
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The Science
How We Calculate Body Composition
Quick Estimate (Deurenberg Formula, BMI-Based)
Body Fat % = (1.20 × BMI) + (0.23 × Age) − (10.8 × sex) − 5.4
sex = 1 for male, 0 for female
Navy Method (Circumference-Based)
Men: BF% = 495 / (1.0324 − 0.19077×log₁₀(waist−neck) + 0.15456×log₁₀(height)) − 450
Women: BF% = 495 / (1.29579 − 0.35004×log₁₀(waist+hip−neck) + 0.22100×log₁₀(height)) − 450
Lean & Fat Mass
Fat Mass = Weight × (Body Fat % ÷ 100)
Lean Mass = Weight − Fat Mass
Worked Example
Step-by-Step Example (Navy Method)
A 30-year-old male, 178 cm tall, 85 kg, with a 38 cm neck and 90 cm waist.
Waist − Neck: 90 − 38 = 52 cm
Apply Navy formula: using log₁₀(52) and log₁₀(178) → BF% ≈ 18.4%
Fat mass: 85 × 0.184 ≈ 15.6 kg
Lean mass: 85 − 15.6 = 69.4 kg
Reference
Body Fat Percentage Categories
Based on the American Council on Exercise classification.
| Category | Men | Women |
|---|---|---|
| Essential Fat | 2-5% | 10-13% |
| Athletes | 6-13% | 14-20% |
| Fitness | 14-17% | 21-24% |
| Average | 18-24% | 25-31% |
| Obese | 25%+ | 32%+ |
How To Measure
Getting Accurate Circumference Measurements
Neck: measure just below the larynx (Adam's apple), tape sloping slightly downward to the front.
Waist: measure at the narrowest point, typically level with your navel, without pulling the tape tight.
Hip (women): measure at the widest point around your hips and buttocks.
Consistency matters: measure at the same time of day (ideally morning, before eating) for comparable results over time.
Who Uses This
Common Ways People Use This Calculator
Healthy Weight Goals
Estimate a healthy body weight for your height.
Fitness Planning
Set realistic weight targets for exercise programs.
Weight Management
Monitor progress while gaining or losing weight.
General Health
Compare your weight with commonly used healthy ranges.
Students
Learn how height and body weight are related.
Healthcare Support
Use estimated weight values during health assessments.
Lifestyle Tracking
Keep an eye on long-term weight changes.
Personal Goals
Plan achievable weight milestones with confidence.
Get More From It
Tips for Accurate Weight Tracking
Weigh Yourself Consistently
Measure your weight at the same time each day, ideally in the morning before eating or drinking.
Wear Similar Clothing
Use lightweight or consistent clothing when weighing yourself to improve accuracy over time.
Use the Same Scale
Different scales may produce slightly different readings, so stick with one reliable scale.
Focus on Long-Term Trends
Daily weight naturally fluctuates due to hydration, meals, and activity. Monitor weekly or monthly trends instead.
Track Height Changes for Children
Growing children should update both height and weight regularly for more meaningful results.
Combine with a Healthy Lifestyle
Use your weight estimate as a guide alongside balanced nutrition, regular exercise, and advice from healthcare professionals.
Questions
Frequently Asked Questions
The Navy Method is generally more accurate since it uses actual body measurements rather than BMI alone, which doesn't account for body shape or fat distribution.
Navy Method typically has an error margin of about 3-4% compared to DEXA scans (the clinical gold standard), which is reasonable for a free at-home method but not lab-precise.
Daily weight fluctuates due to water retention, sodium intake, and digestion — often by 1-2 kg — which can mask your real progress. A moving average smooths this out to show the underlying trend.
At least 3 entries for a basic moving average, though 7 or more (ideally daily) gives a much clearer, more reliable trend line.
Lean body mass is your total body weight minus fat mass — it includes muscle, bone, organs, and water. Preserving lean mass during weight loss is generally a fitness goal.
Yes — falling below essential fat levels (roughly 2-5% for men, 10-13% for women) can impair hormone function and overall health. Very low body fat should be approached under professional guidance.
The Navy Method tends to be more reliable than BMI-based estimates for muscular individuals, since it doesn't penalise extra muscle weight the way BMI does — though it can still be imperfect for extreme physiques.
Monthly is typically sufficient, since body composition changes gradually — measuring more frequently mostly captures measurement noise rather than real change.
No. All calculations, including your Weight Trend Tracker entries, run entirely in your browser for this session — nothing is sent to or stored on our servers.
Men and women tend to store fat differently (more abdominally for men, more in hips for women), so the formula uses hip circumference for women in addition to waist and neck to account for this.
Yes — use "Quick Estimate" mode, which only requires your height, weight, age, and gender. It's less precise than the Navy Method but requires no measurements.
No. Conditions like thyroid disorders, PCOS, or certain medications can affect both weight and body composition — consult a doctor if you have concerns about an underlying condition.
Treat any single reading as an estimate with some margin of error. Tracking the trend over several measurements gives a more reliable picture than one isolated number.
Many sources cite roughly 0.5-1% of body weight per week as a sustainable rate that helps preserve lean mass, though individual circumstances vary — consult a professional for personalised guidance.
Yes, the unit toggle applies to your circumference measurements as well — switch between centimetres and inches at any time before calculating.
No, entries are kept only for your current browser session. If you want a longer-term record, consider noting your moving average trend elsewhere each time you check it.
See Past the Scale
Calculate your body fat and lean mass above, then track your real trend over time.
✓ Navy Method
✓ Lean vs Fat Mass
✓ Smoothed Trend