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Body Fat Calculator

Estimate body fat percentage using the US Navy method. Shows fat and lean mass.

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BMI Calculator

Example 1 — Metric

BMI = 70 ÷ (1.75 × 1.75) = 70 ÷ 3.0625 ≈ 22.9 — Normal weight

Open BMI →

📘 What is the Body Fat Calculator?

Body fat percentage tells you what proportion of your total body weight is fat versus lean mass (muscle, bone, organs, water) — a more meaningful health indicator than weight alone, since two people at the same weight and height can have very different body compositions. This calculator uses the US Navy circumference method, which estimates body fat from simple tape-measure measurements without specialized equipment.

⚙️ How Body Fat % is calculated

The US Navy circumference method

This method uses neck, waist, and (for women) hip circumference measurements, combined with height, in a formula derived from correlation studies against more precise body-composition measurement methods. It is widely used because it requires only a tape measure, making it accessible and repeatable at home.

Why measurement consistency matters more than precision

The circumference method has a margin of error of roughly 3-4% compared to clinical methods (like DEXA scans) when measurements are taken carefully — but this error becomes far less important if you measure the SAME way every time. Measure at the same time of day (ideally morning, before eating), in the same state of hydration, with the tape at the same anatomical landmarks.

Fat mass vs lean mass — both numbers matter

This calculator shows both your estimated fat mass (body fat % × total weight) and lean mass (the remainder) in absolute units, not just the percentage. Tracking lean mass over time is especially useful during weight loss — the goal is typically to preserve or even increase lean mass while fat mass decreases, rather than losing weight indiscriminately.

How body fat ranges relate to health categories

Generally accepted healthy ranges differ by sex (due to essential fat differences) and shift somewhat with age. Ranges are typically presented as bands (e.g., "athletic," "fitness," "average," "above average") rather than a single target number, because individual variation in where fat is healthily distributed is considerable.

🧮 Worked examples

Example 1 — Tracking during a cut

A person starts at 82 kg with an estimated 24% body fat (≈ 19.7 kg fat, ≈ 62.3 kg lean mass). After 3 months they weigh 76 kg with an estimated 19% body fat.

→ New fat mass ≈ 14.4 kg (a loss of ≈ 5.3 kg fat) · New lean mass ≈ 61.6 kg (a loss of only ≈ 0.7 kg) — indicating the weight loss was overwhelmingly fat, not muscle

Example 2 — Same weight, different composition

Two people both weigh 75 kg and are both 175 cm tall. Person A has 15% body fat; Person B has 28% body fat.

→ Person A: ≈ 11.25 kg fat, ≈ 63.75 kg lean mass. Person B: ≈ 21 kg fat, ≈ 54 kg lean mass — identical weight, but nearly double the fat mass and almost 10 kg less lean mass for Person B

Example 3 — Why a small waist-measurement error matters

A 2 cm measurement error on waist circumference for someone with a 85 cm true waist.

→ Because waist circumference has an outsized effect in the formula, a 2 cm error can shift the estimated body fat percentage by roughly 1-2 percentage points — reinforcing why consistent measurement technique matters more than any single reading

💡 Original insights & how to use this calculator

Pairing with BMI for a fuller picture

BMI alone cannot distinguish muscle from fat. If your BMI suggests "overweight" but your body fat percentage falls in a healthy range for your sex and age, body composition — not BMI — is the more accurate indicator. Use this calculator alongside the BMI Calculator whenever BMI results seem inconsistent with how you look or feel.

Setting realistic body fat targets

Very low body fat percentages (associated with visible muscle striations) are difficult to sustain long-term and are typically only maintained temporarily by competitive athletes. For general health, targeting the "fitness" or "average" range for your sex and age is realistic and sustainable for most people — extremely low targets often require restrictive practices that aren't suitable as a permanent lifestyle.

Tracking trend, not single readings

Day-to-day body fat estimates can fluctuate due to hydration, recent meals, and measurement variation. Take measurements weekly or every two weeks at the same time of day, and look at the TREND over 4-8 weeks rather than reacting to any single reading.

Using lean mass to set protein targets

A common guideline for protein intake during fat loss is based on lean body mass rather than total body weight (e.g., roughly 1.6-2.2g of protein per kg of lean mass for those doing resistance training). Once you have an estimated lean mass from this calculator, it can inform a more individualized protein target than total-weight-based rules of thumb.