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Body measurements · FREE & BROWSER-LOCAL

Body-fat calculator

Use height and waist circumference to estimate body-fat percentage with relative fat mass (RFM), plus estimated fat and lean mass from your weight.

Your inputs

These studies used binary sex categories; they do not describe gender identity.
Level tape at the upper border of the right iliac crest, after a normal exhale.

YOUR NUMBERS, EXPLAINED

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How this calculator works

Relative fat mass (RFM) = 64 − 20 × height / waist + 12 × sex, where sex is 0 for the male coefficient and 1 for the female coefficient. Height and waist use the same units. Weight is used for mass results.

Fat mass = body weight × RFM / 100. Lean mass = body weight − fat mass. RFM was developed and validated against DXA using US adult survey data. This circumference estimate is not a military assessment.

Measure standing height without shoes. For waist, locate the upper edge of the right hip bone (iliac crest). Wrap a non-stretch tape horizontally at that level, snug without compressing skin, after a normal exhale. Do not substitute the narrowest waist or navel. Repeat carefully and resolve inconsistent readings.

Waist tape position for RFM A level tape around the torso at the upper border of the hip bone. Top of hip bone Keep tape horizontal
Locate the upper border of the right hip bone, then keep the tape level all the way around. The drawing is schematic; follow the measurement instructions.

Reading your result

Small tape-position changes can move the estimate. Error may be several percentage points and is not a known personal confidence interval. Lean mass includes organs, water and bone as well as muscle. Use consistent measurements; do not interpret small differences as proven fat gain or loss.

Illustrative worked example

With the male coefficient, 175 cm height, 85 cm waist and 70 kg weight: RFM = 64 − 20 × 175 / 85 = 22.8%; estimated fat mass 16.0 kg and lean mass 54.0 kg.

Supported inputs & limitations

Adult use, ages 20–100; height 120–230 cm, waist 40–200 cm and weight 30–300 kg. Not suitable during pregnancy, with altered abdominal anatomy or fluid accumulation. Applicability varies with ancestry, age and body composition, especially very lean or muscular athletes. Nonpositive or ≥100% estimates are rejected, never clamped. No body-fat health categories are assigned.

Sources & methodology

These primary sources support the method and context. They do not endorse helsi or verify this implementation.