Body fat calculator

U.S. Navy (Hodgdon–Beckett) method. This is the tape-measure method the U.S. Navy developed to screen body composition. It uses your height, neck and waist (plus hips for women). Because it reflects where you carry fat, it usually gives a better estimate than BMI, typically within a few percentage points of lab methods.

BMI and age (Deurenberg formula). Body fat % = 1.2 × BMI + 0.23 × age − 10.8 × sex − 5.4 (sex = 1 for men, 0 for women). It needs no tape measure, but it overestimates body fat in muscular people because BMI can't tell muscle from fat. It's for adults 18 and older.

Use a flexible, non-stretch tape. Keep it level and snug against the skin without compressing it, and measure after a normal breath out. Take each measurement two or three times and use the average.

• Neck: just below the larynx (Adam's apple), with the tape sloping slightly down toward the front.
• Waist, men: horizontally at the level of the navel.
• Waist, women: at the narrowest point of the waist.
• Hips, women: around the widest part of the buttocks.

Measure in inches or centimeters; switch the units with the toggle at the top.

The calculator uses the commonly cited American Council on Exercise (ACE) ranges:

Category	Men	Women
Essential fat	2–5%	10–13%
Athletes	6–13%	14–20%
Fitness	14–17%	21–24%
Average	18–24%	25–31%
High (obese range)	25% and up	32% and up

Women naturally carry more essential fat than men, which is why the ranges differ.

If you enter your weight, the calculator splits it into fat mass and lean (fat-free) mass:

• Fat mass = weight × body fat % ÷ 100
• Lean mass = weight − fat mass

Example: 175 lb at 20% body fat is 35 lb of fat and 140 lb of lean mass. Tracking lean mass over time tells you whether a diet is costing you muscle. If your weight drops but your lean mass holds steady, you're mostly losing fat.

A man who is 5 ft 11 in (180 cm) with a 15 in (38 cm) neck and a 35.5 in (90 cm) waist:

Body fat % = 495 ÷ (1.0324 − 0.19077 × log10(90 − 38) + 0.15456 × log10(180)) − 450 ≈ 20%, which is in the average range. The formula uses centimeters; inches are converted for you.

No home method is perfect. Tape measurements depend on technique, and both formulas were built on specific populations. More accurate methods include DEXA scans, hydrostatic weighing and air displacement (Bod Pod). Bioelectrical impedance scales are convenient but can swing with hydration.

The best use of this calculator is tracking your own trend over time with the same method and measuring technique. Pair it with your BMI and waist-to-hip ratio for a fuller picture. It's an informational estimate, not medical advice, and all calculations stay in your browser.