Example Data Table
| Sex |
Age |
Height |
Weight |
Waist |
Neck |
Hip |
| Male |
35 |
178 cm |
82 kg |
91 cm |
39 cm |
95 cm |
| Female |
29 |
165 cm |
64 kg |
74 cm |
32 cm |
96 cm |
| Male |
42 |
70 in |
190 lb |
38 in |
16 in |
40 in |
Formula Used
The calculator uses a linear body fat model based on BMI, age, sex, and circumference correction.
Base formula: Body Fat % = 1.20 × BMI + 0.23 × Age − 10.8 × Sex − 5.4
Sex is 1 for male and 0 for female. BMI is weight in kilograms divided by height in meters squared.
Extended correction: Shape Adjustment = waist-height correction − neck-height correction + optional hip-height correction.
Fat Mass: Weight × Body Fat % ÷ 100
Lean Mass: Weight − Fat Mass
Target Weight: Lean Mass ÷ (1 − Target Body Fat % ÷ 100)
How to Use This Calculator
Select the unit system first. Use centimeters and kilograms for metric mode. Use inches and pounds for imperial mode.
Enter your sex, age, height, weight, waist, neck, and hip values. Use relaxed measurements. Keep the tape level.
Add a target body fat percentage. Choose an activity factor to estimate daily energy needs. Use the advanced adjustment only when you want to calibrate results against a known scan or previous measurement.
Press the calculate button. The result appears above the form. Use the CSV or PDF buttons to save the report.
Understanding Linear Body Fat Estimation
A linear body fat calculator gives a practical estimate from common body measurements. It is useful when a scan, caliper test, or lab method is not available. The method is not a medical diagnosis. It is a maths based guide for tracking change.
Why a Linear Model Helps
A linear model is simple to read. Each input has a clear effect on the final value. BMI adds information from height and weight. Age adds another trend. Sex changes the baseline. Waist, neck, and hip values refine the shape estimate. This makes the result more useful than weight alone.
Measurement Quality Matters
Small tape errors can change the result. Measure the waist at the same point each time. Keep the tape close to the skin, but do not compress it. Measure the neck below the larynx. Measure hips at the widest level. Use the same unit system for every field.
Using the Result
The result includes body fat percentage, fat mass, lean mass, BMI, and target weight. Fat mass shows estimated stored fat. Lean mass includes muscle, bone, water, and organs. Target weight is based on keeping lean mass stable. Real changes can differ because hydration and training affect scale weight.
Planning With the Estimate
Use the estimate as a trend tool. Compare results over several weeks. A single reading can be noisy. A steady pattern is more helpful. If body fat falls while lean mass stays stable, the plan may be working. If lean mass drops quickly, calorie intake or training may need review.
Best Use Cases
This calculator works well for personal logs, coaching notes, classroom maths examples, and fitness planning. It gives clear numbers without complex equipment. For clinical decisions, use professional assessment. For everyday tracking, consistent measurements are often more valuable than perfect precision.
FAQs
1. What is a linear body fat calculator?
It estimates body fat percentage with a formula that uses BMI, age, sex, and body measurements. The output is an estimate, not a medical diagnosis.
2. Which unit system should I use?
Use metric for centimeters and kilograms. Use imperial for inches and pounds. Do not mix units in one calculation.
3. Why does waist size affect the result?
Waist size helps estimate fat distribution. A higher waist-to-height ratio usually increases the estimated body fat percentage.
4. Why is neck size included?
Neck size helps balance the circumference estimate. In this model, a larger neck compared with height can reduce the shape correction.
5. Should women enter hip measurement?
Yes. Hip measurement improves the shape correction for female estimates. Men can also enter it, but it has less effect here.
6. What does target weight mean?
Target weight estimates body weight at your chosen body fat percentage, assuming lean mass stays the same.
7. Can I export the result?
Yes. After calculation, use the CSV or PDF button above the form to download your result.
8. Is this calculator accurate for athletes?
It may be less accurate for very muscular athletes. Use the advanced adjustment if you have a trusted reference result.