Body Fat Calculator: Estimate Your Body Fat Percentage Free and Privately
A body fat calculator estimates what share of your body weight is fat. Pick a method above (US Navy, Relative Fat Mass or BMI-based), choose Male or Female, enter your measurements, and the calculator returns a body fat percentage, its American Council on Exercise (ACE) category and, if you add your weight, your fat mass and lean body mass. It is an estimate that can differ from a DXA scan by several percentage points.
The calculation runs in your browser and nothing is uploaded; you can check the Network tab in DevTools. Only the Save to history button stores anything, in your browser's local storage.
The three formulas (lengths in centimetres)
- US Navy (Hodgdon and Beckett, 1984), men: 495 ÷ (1.0324 − 0.19077 × log₁₀(waist − neck) + 0.15456 × log₁₀(height)) − 450. Women: 495 ÷ (1.29579 − 0.35004 × log₁₀(waist + hip − neck) + 0.221 × log₁₀(height)) − 450.
- Relative Fat Mass (Woolcott and Bergman, 2018): 64 − 20 × height ÷ waist, plus 12 for women.
- BMI-based (Deurenberg and colleagues, 1991): 1.2 × BMI + 0.23 × age − 10.8 × sex − 5.4, where sex is 1 for men and 0 for women.
Inches and pounds are converted first, and the percentage is rounded to one decimal before its category is chosen.
Body Fat Calculator Table of Use: Inputs and Results
| Method | You enter | You get |
|---|---|---|
| Navy, man | 175 cm, waist 85, neck 38, weight 75 kg | 16.9%, Fitness; fat mass 12.7 kg, lean mass 62.3 kg |
| Navy, woman | 165 cm, waist 75, neck 32, hip 98, weight 62 kg | 28.9%, Average; fat mass 17.9 kg, lean mass 44.1 kg |
| RFM, man | 175 cm, waist 85 (weight optional) | 22.8%, Average |
| BMI-based, man | 175 cm, 75 kg, age 30 | 20.1%, Average |
| Tracking | Save to history after each measurement | Up to 50 records in this browser, latest 10 listed |
Body Fat Calculator Features
- Three methods: the form shows only the fields each needs. Navy asks for neck and waist, plus hip for women; RFM asks for waist only; BMI-based asks for weight and age.
- Units: cm / kg or in / lbs, with typed values converted (rounded to one decimal) when you switch. A decimal comma is accepted.
- Measuring hints: each field says where to place the tape, such as navel level for a man's Navy waist or just below the Adam's apple for the neck.
- ACE category and scale: six categories from Below essential fat to Obese, with separate cut-offs for men and women and a bar running to 45%.
- Fat and lean mass: shown whenever a weight is entered; weight is optional for Navy and RFM.
- Sanity checks: unrealistic measurements (for example height outside 100 to 250 cm), ages under 18 for the BMI-based method, and results above 70% or below 0% are refused with a message instead of a number.
- Copy and history: Copy gives a text summary; Save to history keeps up to 50 records with delete and Clear all.
It is not a medical device and does not replace DXA, hydrostatic weighing or a clinician. For a weight-based screen, use the BMI Calculator.
How to Use the Body Fat Calculator
- Under Calculation method, press Navy method, RFM or BMI-based.
- Press Male or Female, and cm / kg or in / lbs.
- Fill in the fields shown, such as Height (cm), Waist (cm) and Neck (cm). Measure two or three times and use the average.
- Optionally add Weight for fat and lean mass. The BMI-based method also needs Age (years).
- Read the percentage and category under Results, then press Copy or Save to history.
Who Can Use the Body Fat Calculator
Adults who train, diet or want a number beyond the scale can use it, as can anyone without access to a DXA scan. Compare readings only within one method.
To go further, the Calorie Calculator estimates daily energy needs and the Ideal Weight Calculator compares your height with published formulas. Convert tape readings with the Length Converter, Weight Converter or Unit Converter, work out the change between two readings with the Percentage Calculator, and find your whole-year age with the Age Calculator. The Scientific Calculator helps check the logarithms by hand.
Body Fat Calculator FAQs
How do I calculate my body fat percentage at home?
Choose "Navy method", pick Male or Female, then enter height, neck and waist (and hip for women) measured with a flexible tape. A man 175 cm tall with a 38 cm neck and an 85 cm waist gets 16.9%, which is "Fitness" on the ACE scale. Add your weight to see fat mass and lean body mass.
Which body fat method should I use?
If you own a tape measure, use the Navy method or RFM, which rely on body measurements; RFM needs only height and waist. The BMI-based formula needs no tape but cannot tell muscle from fat, so it tends to overestimate in muscular people. All three are estimates that can differ from a DXA scan by several percentage points.
How do I measure my waist, neck and hips correctly?
Hold a flexible tape level, snug but not squeezing. For the Navy method, men measure the abdomen at navel level and women the narrowest point of the waist; the neck goes just below the Adam's apple and women also measure the widest point of the buttocks. For RFM, measure just above the hip bones after breathing out.
What is a healthy body fat percentage?
As of October 2026, the American Council on Exercise (ACE) classes 14 to 17% as fitness and 18 to 24% as average for men, and 21 to 24% as fitness and 25 to 31% as average for women. Obese starts at 25% for men and 32% for women. Essential fat is about 2 to 5% for men and 10 to 13% for women.
Why do the three methods give different results?
Each formula was built on a different group of people and uses different inputs. For the same man, 175 cm, 75 kg, 30 years old, with an 85 cm waist and 38 cm neck, the calculator gives 16.9% (Navy), 22.8% (RFM) and 20.1% (BMI-based). Use one method consistently when tracking.
What are fat mass and lean body mass?
Fat mass is your weight multiplied by your body fat percentage, and lean body mass is everything else: muscle, bone, organs and water. At 80 kg and 20% body fat, fat mass is 16 kg and lean body mass is 64 kg. Weight is optional for the Navy and RFM methods and is used only for these two figures.
Is my data stored or uploaded?
Nothing is uploaded. The calculation runs in your browser. If you press "Save to history", the date, body fat percentage, method and weight (if entered) are kept in your browser's local storage on this device, up to 50 records, and you can delete one record or press "Clear all" at any time.