Body fat calculator
Enter the requested body measurements to obtain a tape-based body-fat estimate and calculated masses.
Read the method and measurement instructions. An equation estimate is not a scan.
Start with the measure
Body composition.
Body composition describes the components of your body weight, such as fat mass and fat-free mass. Weight, a waist measurement and an estimated body-fat percentage answer different questions. Choose what you want to follow, then learn what the number actually represents. [1]
Find your starting point
01 / Choose the question
What brought you here?
Use the question in front of you to choose the next resource.
I want to choose a measurement.
Separate a direct measurement from a component estimated using a model.
Compare the outputsI already have numbers.
Find the calculator that uses your inputs, and check what its result can tell you.
Open the toolsI want to understand a goal.
Find the planned guides on recomposition, percentages and the language used around body shape.
Explore guide topics02 / Read the output
Three kinds of number, three different uses.
Keep the measurement and the estimate visible when you compare results.
| Starting point | What you have | What to check |
|---|---|---|
| Weight or circumference | Total mass or a body dimension. | The same measurement does not directly separate fat, water and skeletal muscle. |
| A body-fat estimate | An estimate derived from a method, such as skinfolds, impedance or a circumference equation. | The equation, its reference population, the device and the measurement conditions. [2] |
| A scan report, such as DXA | Outputs for components such as fat, lean soft tissue and bone mineral. | The report's definitions. Fat-free mass, lean soft tissue and skeletal muscle are distinct terms. [1] |
Fat-free mass is broader than skeletal muscle. It includes water, proteins and minerals throughout the body. A number labeled “lean” needs its definition checked before you treat it as a muscle measurement. [1]
Ask what was measured and what was calculated. The 2018 methods review describes different assumptions and sources of error across techniques. Choose a method around its purpose and how it can be repeated. [2]
03 / Keep the input in view
A percentage becomes calculated masses.
The two-component model separates body weight into fat mass and fat-free mass. The calculation still depends on the body-fat estimate you enter. [1]
Values are rounded for the example; pound conversions use the NIST conversion factor. [5]
04 / Available now
Choose a tool for the calculation you need.
These five tools are available on the site. Their results depend on the inputs and assumptions; they do not replace a body-composition assessment.
Lean body mass calculator
Compare height-and-weight equation estimates, or calculate from a supplied body-fat percentage.
The tool's “lean body mass” title does not make its result a direct measurement of skeletal muscle.
FFMI calculator
Calculate fat-free mass in relation to height using your supplied weight and body-fat percentage.
An uncertain body-fat input carries through to the index. Read the calculation separately from any benchmark label.
Body recomposition calculator
Explore the energy and protein targets calculated from your activity, training and strategy inputs.
Treat the outputs as modeled intake targets; they do not forecast changes in fat or skeletal muscle.
Waist-to-hip ratio calculator
Divide waist by hip circumference; the optional height input also produces a waist-to-height ratio.
A circumference ratio does not directly measure visceral fat. A health interpretation needs appropriate context.
05 / Explore the collection
Find the guide topic behind your question.
The detailed guides below are in preparation. Their titles will become links when they are available; the five calculators above can already be opened.
Measurement and interpretation
Understand the method and the label.
These topics will compare assessment methods and explain how percentage charts and appearance-related terms should be read.
- How to measure body fat
- Reading a body-fat percentage chart
- Understanding the “skinny fat” label
Training goals
Keep the goal separate from the estimate.
A measurement describes an output. Planning a change in fat or muscle involves a different question.
- Body recomposition
- Abdominal definition
06 / Read results with care
A useful number needs a clear meaning.
Does an accurate weight reading validate a smart scale's body-fat estimate?
In a 2021 study, three connected scales were compared with DXA in adult patients referred to a French hospital unit for assessment. Weight readings agreed more closely with the reference than the scales' fat-mass estimates. The models tested and the patient population matter; this study does not rank all current scales or establish how well they track one person's change over time. [4]
What should I record when I compare results?
Record the method, device, units and how the measurement was taken. Skinfold estimates can be affected by technique and the equation used; hydration and other preparation factors can affect impedance estimates. Keep the conditions as comparable as the method allows, rather than treating a device change as a change in your body. [2]
What are the “five levels” of body composition?
Wang, Pierson and Heymsfield's research framework describes atomic, molecular, cellular, tissue-system and whole-body levels. These are levels of biological organization, not five health or fitness ratings. Compartment models, such as fat mass plus fat-free mass, describe a different part of the framework. [3]
Can one percentage tell me whether I am healthy?
Read the method, its assumptions and the context before interpreting a number. If the result is being used for a medical decision or worries you, ask a qualified healthcare professional which assessment is appropriate. This collection does not set an individual body-fat target.
Sources
Read the evidence behind the terms.
- Prado CM, et al. Methodological standards for body composition: levels, models and terminology (2025). Adult body-composition definitions and interpretation. PMID 40754386; DOI 10.1016/j.ajcnut.2025.05.022.
- Kuriyan R. Body composition techniques. Indian Journal of Medical Research (2018). Methods, assumptions and sources of measurement error. PMID 30666990.
- Wang ZM, Pierson RN Jr, Heymsfield SB. The five-level model of body-composition research (1992). Original model; PubMed abstract. DOI 10.1093/ajcn/56.1.19.
- Frija-Masson J, et al. Accuracy of Smart Scales on Weight and Body Composition (2021). Cross-sectional study of three models in hospital patients. DOI 10.2196/22487.
- NIST Guide to the SI, Appendix B.8. Mass-unit conversions.
Prepared with AI assistance by the Fitness Instructor AI Editorial Team. Updated . Read our editorial policy.