Body Fat Calculator
ForgePlug's Body Fat Calculator is a premium body-composition dashboard. Estimate your body-fat percentage with the US Navy circumference method or the Jackson-Pollock skinfold method (3-site or 7-site, with the Siri equation), compare against a BMI-based estimate, and instantly see lean body mass, fat mass, and your ACE health category. Interactive charts — a live gauge, body-composition donut, category progress bar, and method comparison — update as you type. Includes an interactive measurement guide, smart insights, education, and export (PDF, CSV, copy, print). Works fully offline after first load, supports metric & imperial units, and never uploads your data.
Your Measurements
Estimates body fat from neck, waist, and (for women) hip circumferences compared with height. The standard field method used by the US military.
Units
Sex
Circumference Measurements
All calculations happen entirely inside your browser. Your measurements are never uploaded or stored on our servers.
Body Fat
17.3%
Average
Lean Body Mass
64.5kg
83% of weight
Fat Mass
13.5kg
17.3% of weight
Healthy Category
Average
ACE classification (male)
This calculator provides an estimate using the U.S. Navy circumference method. Results are typically accurate within approximately ±3–4% compared with laboratory methods such as DEXA scans. It is intended for educational purposes only and should not be considered a medical diagnosis. Consistent measurements over time are generally more meaningful than a single reading.
Body Fat Gauge
17.3%
average category
Body Composition
17.3%
body fat
Lean Mass
83%
Fat Mass
17.3%
Lean vs Fat (kg)
64.5 / 13.5 kg
ACE Category Position
Method Comparison
US Navy MethodCurrent
17.3%
Direct measurement estimate
BMI Estimate
20.2%
From BMI, age & sex
Ideal (Fitness)
—
Fitness range: 14–17%
Athlete
—
Athlete range: 6–13%
The US Navy Method and BMI estimate differ by 2.9 points because BMI cannot distinguish muscle from fat — body composition can vary widely at the same BMI.
Smart Insights
Within the Average range
Your estimated body fat of 17.3% is in the Average category for your sex. Consistent tracking over time is more meaningful than any single reading.
Lean body mass
Lean body mass represents approximately 83% of your total body weight (≈64.5 kg).
Method comparison
The BMI estimate reads 2.9 points higher than the Navy method — expected when muscle mass is higher than average, since BMI cannot distinguish muscle from fat.
Consistency beats perfection
Body-fat estimates are most useful when tracked consistently over time with the same technique. If your goal is fat loss, prioritise preserving lean mass through protein and strength training.
Educational estimate
This tool provides an estimate (US Navy circumference, Jackson-Pollock skinfold, or BMI). It is educational and never a substitute for a medical diagnosis.
Export Report
Summary Preview
Body Fat Calculator — Summary ============================== Method: US Navy Method Sex: male · Age: 30 years Height: 178 cm · Weight: 78 kg Neck: 38 cm · Waist: 86 cm Body fat: 17.3% Category (ACE): Average Fat mass: 13.5 kg Lean body mass: 64.5 kg BMI comparison BMI: 24.6 (Healthy) BMI body-fat estimate: 20.2% Difference (Navy − BMI): -2.9 points All calculations happen entirely inside your browser. This is educational information, not medical advice.
Measurement Guide
Accurate, consistent measurements are the key to a trustworthy estimate.
- 1Stand straight with shoulders relaxed and head facing forward.
- 2Place the tape just below the larynx (Adam's apple).
- 3Keep the tape level all the way around, sloping slightly downward at the front.
- 4Record the measurement at the end of a normal breath.
💡 Don't pull the tape tight enough to compress the skin.
💡 Look straight ahead — tilting your chin changes the reading.
Example: most adults measure 30–45 cm (12–18 in).
Your Measurements
Estimates body fat from neck, waist, and (for women) hip circumferences compared with height. The standard field method used by the US military.
Units
Sex
Circumference Measurements
All calculations happen entirely inside your browser. Your measurements are never uploaded or stored on our servers.
Health Education
Understand what these numbers mean — and why they matter.
Body-fat percentage is the mass of fat tissue divided by total body mass. It gives a far clearer picture of health than weight alone.
Fat is essential — it stores energy, insulates the body, and supports hormones. Essential fat levels are roughly 2–5% for men and 10–13% for women.
Beyond essential levels, excess body fat is associated with increased cardiometabolic risk, while extremely low levels can impair hormonal and immune function.
Why this calculator gives you two numbers, not one
The Navy method and the skinfold method measure different things and can legitimately disagree.
Body fat percentage matters more than weight or BMI alone because two people at the same height and weight can have very different amounts of muscle versus fat — and that difference is exactly what BMI can't see. This calculator gives you three independent estimates side by side (US Navy circumference, Jackson-Pollock skinfold, and a BMI-based estimate) precisely so you're not trusting a single number that happens to be wrong for your body type.
How to use it
- Choose metric or imperial units and enter your sex, age (optional), height, and weight.
- For the Navy method, measure your neck just below the larynx, your waist at the navel (men) or narrowest point (women), and — for women — your hips at the widest point. Use the interactive measurement guide if you're unsure of tape placement.
- For the Jackson-Pollock skinfold method, switch protocols to 3-site or 7-site, then enter the caliper readings in millimeters for each site (chest, abdomen, thigh for men; triceps, suprailiac, thigh for women, plus more sites in the 7-site protocol).
- Read your live dashboard: body-fat percentage, lean body mass, fat mass, and ACE health category update instantly as you type, with a method-comparison chart showing how the Navy, skinfold, and BMI estimates line up against each other.
- Export your results as a PDF or CSV, or print a summary, once you're happy with the numbers.
Common use cases
- Tracking body recomposition — using the same method consistently (Navy or skinfold, not switching between them) to see whether you're losing fat and keeping muscle during a diet or training block.
- A quick estimate with no equipment — the Navy method only needs a tape measure, making it the practical default when you don't own skinfold calipers.
- Cross-checking a gym or trainer reading — comparing a skinfold reading someone else took against your own Navy-method estimate, and understanding why a few points of difference is normal, not a sign either measurement is wrong.
- Understanding what BMI is missing — seeing your BMI-based estimate next to the more direct methods makes it concrete why BMI alone can misclassify muscular or very lean people.
Frequently Asked Questions
Everything you need to know about body fat, the Navy method, and accuracy
How accurate is the US Navy body fat method?
What is a healthy body fat percentage?
How do I measure my neck, waist, and hips correctly?
Why does the BMI estimate differ from the Navy method?
What is the Jackson-Pollock skinfold method?
Do I need skinfold calipers to use this method?
Which method is most accurate: Navy, skinfold, or BMI?
Is my body fat data private?
Does this calculator work on mobile?
Tool Overview
A closer look at Body Fat Calculator — how it works, who it's for, and where it fits in your workflow.
Body fat percentage is a more meaningful health metric than weight alone — two people at the same weight can have very different body compositions, and your fat percentage is a better predictor of metabolic health. The Body Fat Calculator estimates your percentage using two validated methods: the US Navy circumference method (using neck, waist, and hip measurements) and the Jackson-Pollock skinfold method with 3-site or 7-site caliper measurements.
The US Navy method is the most accessible — it only requires a measuring tape and takes seconds. The Jackson-Pollock method is more precise when you have calipers, and the calculator supports both 3-site (for quick checks) and 7-site (for higher accuracy) protocols, applying the Siri equation to convert skinfold totals to body fat percentage. A BMI-based comparison provides a rough reference, and the results show lean body mass, fat mass, and your ACE health category. Interactive charts — a live gauge, body-composition donut, category progress bar, and method comparison — make the numbers easy to understand at a glance.
Body measurements are among the most private health data you can have, which is why every calculation runs entirely in your browser. Nothing is uploaded, no account is required, and the tool works offline. The measurement guide includes interactive diagrams so you can take accurate measurements without guessing.
Key Features
Everything you get with this tool, at a glance.
US Navy Method
Circumference-based estimation using neck, waist, and hip measurements.
Jackson-Pollock Skinfold
3-site or 7-site caliper method with the Siri equation.
BMI Comparison
Rough body-fat estimate from BMI for comparison purposes.
Lean & Fat Mass
See your estimated lean body mass and fat mass in kg or lbs.
ACE Health Categories
Essential, athletic, fit, acceptable, or obese — with color-coded feedback.
100% Private & Local
All calculations run in your browser — no uploads, no sign-up.
How to Use Body Fat Calculator
Get from zero to done in four quick steps — no account, no learning curve.
Choose a method
Pick US Navy (tape measure) or Jackson-Pollock (calipers) — or try both.
Enter your measurements
Input neck, waist, and hip (Navy) or skinfold sites (Jackson-Pollock).
Review the dashboard
See your body fat percentage on the live gauge, with lean mass and fat mass.
Check the category
See your ACE health category — essential, athletic, fit, acceptable, or obese.
Practical Examples
Real input and output pairs so you know exactly what to expect.
US Navy method
Input
Male · 175cm · Neck: 38cm · Waist: 85cm
Output
Body fat: ~18% · Lean mass: 61.5 kg · Fat mass: 13.5 kg · ACE: Fit
Jackson-Pollock 3-site
Input
Male · Chest: 12mm · Abdomen: 20mm · Thigh: 15mm
Output
Body fat: ~16% · Siri equation · 3-site protocol
Method comparison
Input
Same person: Navy vs Jackson-Pollock vs BMI estimate
Output
Navy: 18% · JP: 16% · BMI estimate: 20% — three reference points
Guides & Articles
Learn how to get the most out of this tool with our in-depth guides.
Understanding BMI's Limits and What to Use Instead
BMI is the most widely used health number in the world — and the most widely misunderstood. Here's what it can tell you and what it can't.
How BMI Is Calculated and What the Number Really Means
BMI is one number computed from height and weight — here's the formula, a worked example, and the honest limits of what it can tell you.
Part of Health & Fitness
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