Body fat percentage tells you how much of your weight is fat versus everything else — muscle, bone, water, and organs. It's often a more meaningful health signal than weight alone, and you can get a reasonable estimate without a gym scan or skinfold calipers. Here's how the math works and what the numbers mean.
What "body fat percentage" measures
Your body is made of fat mass and lean mass. Body fat percentage is simply:
Body fat % = (fat mass ÷ total body weight) × 100
A clinically precise reading needs tools like DEXA scans or hydrostatic weighing. But for everyday tracking, a formula-based estimate using numbers you already have works surprisingly well.
The Deurenberg estimate
A common at-home method derives body fat from your BMI, age, and sex (the Deurenberg formula):
Body fat % = (1.20 × BMI) + (0.23 × age) − (10.8 × sex) − 5.4
Here sex is 1 for men and 0 for women, and BMI = weight(kg) ÷ height(m)².
Worked example — a 35-year-old man, 80 kg, 1.78 m tall:
- BMI = 80 ÷ (1.78²) = 80 ÷ 3.17 ≈ 25.2
- (1.20 × 25.2) = 30.3
- (0.23 × 35) = 8.05
- (10.8 × 1) = 10.8
- 30.3 + 8.05 − 10.8 − 5.4 ≈ 22.1% body fat
Healthy ranges to compare against
Because women naturally carry more essential fat, ranges differ by sex (American Council on Exercise guidelines):
Men
- Essential fat: 2–5%
- Athletes: 6–13%
- Fitness: 14–17%
- Average: 18–24%
- Obese: 25%+
Women
- Essential fat: 10–13%
- Athletes: 14–20%
- Fitness: 21–24%
- Average: 25–31%
- Obese: 32%+
Our example man at 22.1% lands in the average range — healthy, with room to lean out if that's his goal.
How to use it
The quickest route is the Body Fat Calculator. Enter your height, weight, age, and sex, and it applies the formula and shows where you fall against the healthy ranges above.
Because this method is built on BMI, it's worth checking your raw BMI Calculator result too — a very muscular build can inflate both numbers. To set a concrete target, the Ideal Weight Calculator gives a healthy weight range for your height that pairs naturally with a body-fat goal.
Keep expectations realistic
Formula-based estimates are convenient but approximate; they can be off by several percentage points, especially for very lean or very muscular people. The most useful approach is consistency — measure the same way over time and watch the trend rather than obsessing over any single reading.
These numbers are general estimates and not medical advice. For a precise assessment or if you have health concerns, consult a qualified professional.