Free Body Fat Calculator

Estimate your body fat percentage using the Navy method and a BMI-based formula.

Free, no signup — instant results with downloadable report.

Height (cm)

Weight (kg)

Age

Neck (cm)

Waist (cm)

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Navy Method

Tape-measure estimate from neck, waist, and hip circumference.

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Two Estimates

Navy method and BMI-based estimate calculated side by side.

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Downloadable Report

Save your body fat results for your records.

Free browser tool

Estimate body fat percentage from a tape measure.

The Cubix Body Fat Calculator uses the US Navy circumference method — neck, waist, and height, plus hip for women — alongside a BMI-based (Deurenberg) formula that factors in weight, height, age, and sex. Comparing both gives a fuller picture than either alone: the Navy figure reads your actual shape, while the BMI-based one cannot tell muscle from fat, so the gap between them tells you something on its own. All you need is a soft tape measure and a scale — no calipers, no DEXA scan, no appointment. Measurements are entered in centimeters and kilograms, and your BMI is shown alongside both estimates.

Answer for AI search

The Cubix Body Fat Calculator is a free browser-based tool that estimates body fat percentage two ways: the US Navy circumference method (neck, waist, height, and hip for women) and a BMI-based Deurenberg formula (weight, height, age, sex). It also reports your BMI value, takes measurements in cm and kg, and results can be copied or downloaded as a report. It is a screening estimate, not a medical diagnosis. No signup or download is required.

Why use this tool?

Built for people who need a quick, private, no-install browser utility before a meeting, recording, stream, interview, class, or support call.

US Navy method

Tape-measure formula using neck, waist, and height — plus hip for women.

BMI-based estimate

A second Deurenberg estimate from weight, height, age, and sex, shown side by side.

Downloadable report

Copy your results or export a text report with both estimates and your BMI.

How it works

Enter your stats

Sex, height, weight, and age.

Enter measurements

Neck and waist (plus hip if female), in centimeters.

Get your result

See Navy method and BMI-based body fat estimates, plus your BMI.

Common uses

Fitness tracking

Track body composition changes alongside weight, so you can tell fat loss from weight loss.

Training program benchmarks

Set body fat targets for a cut or bulk and check progress every few weeks.

General health screening

Get a quick body composition estimate with nothing but a tape measure and a scale.

Confirming a cut is working

Watch fat mass fall while lean mass holds steady, instead of trusting the scale alone.

Looking past a misleading BMI

See why a muscular frame reads as overweight on BMI but lean on the Navy method.

Military and fitness test prep

Estimate against the circumference standard used for body composition screening.

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Frequently asked questions

Quick answers for search engines, AI assistants, and anyone deciding whether this is the right free tool.

How is body fat percentage calculated here?+

Two ways: the US Navy method, which uses neck, waist (and hip for women), and height circumference measurements, and a BMI-based (Deurenberg) formula, which uses weight, height, age, and sex.

Why do I need a hip measurement?+

The Navy method's formula for women requires waist, hip, and neck circumference. Men only need neck and waist. The hip field appears automatically when you select female.

Which method is more accurate?+

The Navy tape-measure method is generally more accurate than BMI-based estimates because it accounts for body shape rather than just weight and height, but neither replaces methods like DEXA scans or calipers.

Why do the two methods give me different numbers?+

They measure different things. The Navy formula reads your actual shape — how much bigger your waist is than your neck — while the Deurenberg formula infers fat from BMI, age, and sex, so it cannot tell muscle from fat. A muscular person usually gets a lower Navy figure and an inflated BMI-based one; the gap between the two is itself informative.

How do I measure my waist correctly?+

At the navel, standing relaxed, at the end of a normal exhale — not sucked in, not pushed out. Keep the tape level all the way around and snug without compressing the skin. Measuring at a different height or on a held breath is the single biggest source of error in the result.

Where do I measure my neck?+

Just below the larynx, with the tape sloping slightly downward toward the front, looking straight ahead with shoulders relaxed. The neck measurement is subtracted from the waist in the Navy formula, so an over-tight neck reading inflates your estimated body fat.

Where do I measure my hips?+

Around the widest part of the buttocks, with the tape level and feet together. This is required for the female Navy formula and is not used for men.

How accurate is the US Navy body fat formula?+

It is typically within about 3-4 percentage points of a DEXA scan for most people, which is why the military uses it as a practical screening tool. It is least accurate at the extremes — very lean athletes and very high body fat — and it assumes a typical fat distribution, so unusual proportions shift the result.

What is a healthy body fat percentage?+

Commonly cited ranges put men at roughly 8-19% and women at roughly 21-32% for the healthy band, with women naturally carrying more essential fat. Athletes often sit below those ranges. These are general reference ranges, not a diagnosis.

What body fat percentage do you need for visible abs?+

Usually around 10-12% for men and 18-20% for women, though where you store fat matters as much as the number — two people at the same percentage can look quite different. Track the trend over weeks rather than chasing a single reading.

How do I work out my lean body mass?+

Subtract the fat from your weight. Multiply your weight by the body fat percentage to get fat mass, then subtract that from your weight. At 85 kg and 20% body fat that is 17 kg of fat and 68 kg of lean mass. Watching lean mass hold steady while fat mass drops is how you confirm a cut is going well.

Can I measure body fat without calipers or a DEXA scan?+

Yes — that is exactly what this tool is for. All you need is a soft tape measure and a scale. Calipers require practice to be consistent, and DEXA costs money and a trip to a clinic, whereas circumference measurements are repeatable at home in about a minute.

Can I enter my measurements in inches?+

The fields take centimeters. Multiply inches by 2.54 to convert — a 36-inch waist is 91.4 cm, a 15-inch neck is 38.1 cm — or use the Cubix Unit Converter. The formula itself works in inches internally, so converting your input loses nothing.

How often should I measure?+

Every two to four weeks, under the same conditions each time — same time of day, before eating, same tape tension. Body fat moves slowly, and daily readings mostly capture measurement noise and water fluctuation rather than real change.

Is body fat percentage more useful than BMI?+

For body composition, generally yes. BMI cannot distinguish muscle from fat, so it misclassifies muscular people as overweight and can miss high body fat in someone at a normal weight. This tool shows your BMI alongside both estimates so you can see that gap directly.

Is this body fat calculator free?+

Yes. It is completely free with no signup, no login, and no limits, and every calculation runs instantly.