Estimates from general formulas, not medical advice. Check with a doctor before big changes to diet or training.
No tape measure? The Deurenberg (1991) formula estimates body fat from BMI, age and sex: 1.2 × BMI + 0.23 × age − 10.8 × sex − 5.4, where sex is 1 for men and 0 for women. A 40-year-old man with a BMI of 25 gets about 23%. It is rougher than the tape method and overestimates fat in muscular people.
How to use
- Pick a calculator in the tabs and choose metric or imperial units; the choice is remembered.
- Body fat: measure your neck below the larynx, your waist at the navel (men) or narrowest point (women) and hips at the widest point, then enter them. Or switch to From BMI.
- Ideal weight: enter height and sex. One-rep max: enter the weight and reps of a hard set. Calories: pick an activity and minutes. Water: weight and daily exercise. Steps: step count and your height or stride.
- Results update as you type. Tap any result to copy it.
- The US Navy method (Hodgdon and Beckett, 1984) is usually within 3–4 percentage points of a DEXA scan. The BMI method (Deurenberg, 1991) is rougher and overestimates fat in muscular people.
- Ideal weight formulas were made for drug dosing, not as health targets; the BMI range is a broader guide.
- 1RM: Epley = w × (1 + reps/30), Brzycki = w × 36 / (37 − reps), Lombardi = w × reps^0.10. All are most accurate for 2 to 10 reps.
- Calories use MET × weight (kg) × hours from the Compendium of Physical Activities and include your resting burn. Fitness trackers and machines may show different numbers.
- Water: about 35 ml per kg plus exercise. Food covers roughly 20% of water intake; EFSA suggests about 2.0 L a day for women and 2.5 L for men from all sources.
The US Navy method
Developed by Hodgdon and Beckett in 1984, it uses height and circumferences. Measure the neck just below the larynx, the waist at the navel for men or at the narrowest point for women, and the hips at the widest point. It is usually within 3–4 percentage points of a DEXA scan, which is good for a tape measure.
Take each measurement twice, keep the tape level and snug but not tight, and measure at the same time of day to track changes.
What the numbers mean
ACE categories for men: essential fat 2–5%, athletes 6–13%, fitness 14–17%, average 18–24% and obese 25% or more. For women: essential 10–13%, athletes 14–20%, fitness 21–24%, average 25–31% and obese 32% or more. Women naturally carry more essential fat.
Fat mass = weight × body fat %, and lean mass is the rest. These are estimates from general formulas, not medical advice. Nothing you enter leaves your device.
Frequently asked questions
How do I measure body fat at home?
Use a tape measure: neck, waist and, for women, hips, then enter them with your height. The US Navy formula turns them into a body fat percentage.
How accurate is the US Navy body fat formula?
Typically within 3–4 percentage points of DEXA for most people. Errors are larger with very high or very low body fat or careless measuring.
What is a healthy body fat percentage?
ACE lists 14–24% as fitness to average for men and 21–31% for women. Lower is not always better; essential fat is needed for health.
Why do women have a higher body fat percentage?
Women carry more essential fat for hormonal and reproductive functions, so every category starts about 8–10 points higher.
Can I estimate body fat without a tape measure?
Yes, with the BMI method, but it is rougher and overestimates fat in muscular people.