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FFMI Calculator

Estimate fat-free mass index, normalized FFMI, fat-free mass, and fat mass from height, weight, and body fat percentage.

Enter pounds for imperial or kilograms for metric.

Enter total inches for imperial or centimeters for metric.

Enter estimated body fat percentage.

Status: initial

Results

Awaiting calculation

Fitness guide

Introduction

The FFMI Calculator estimates fat-free mass index from height, weight, and body fat percentage. It also shows normalized FFMI, fat-free mass, and fat mass for fitness tracking context.

Purpose

Use this calculator to understand lean mass relative to height. FFMI can be useful for fitness progress tracking, but it should not be used as a medical diagnosis or proof of training status.

How FFMI is calculated

The calculator estimates fat-free mass from body weight and body fat percentage, divides fat-free mass by height squared, and applies a height normalization adjustment.

Variable explanations

Unit system

Choose imperial for pounds/inches or metric for kilograms/centimeters.

Weight

Current body weight in the selected unit system.

Height

Total height in inches for imperial or centimeters for metric.

Body fat percentage

Estimated body fat percentage from a method such as DEXA, calipers, smart scale, or visual estimate.

Formula and method guide

Fat-free mass

Fat-free mass = weight x (1 - body fat percentage)

  • Weight is converted to kilograms.
  • Body fat percentage is entered as a percent.

Fat-free mass is all body mass that is not fat mass.

FFMI

FFMI = fat-free mass / height²

  • Fat-free mass is in kilograms.
  • Height is in meters.

FFMI compares lean mass to height.

Normalized FFMI

Normalized FFMI = FFMI + 6.3 x (1.8 - height)

  • Height is in meters.
  • 1.8 meters is the reference height.

Normalized FFMI adjusts the score for height differences.

Worked examples

Imperial example

  1. Choose imperial.
  2. Enter 180 lb, 70 inches, and 15% body fat.
  3. Review FFMI and normalized FFMI.

Metric example

  1. Choose metric.
  2. Enter 82 kg, 178 cm, and 15% body fat.
  3. Compare fat-free mass and FFMI.

Progress tracking

  1. Use the same measurement method each time.
  2. Compare FFMI over time.
  3. Avoid overreading small changes.

Body fat sensitivity

  1. Keep height and weight the same.
  2. Change body fat percentage.
  3. Notice how FFMI depends heavily on body fat estimate accuracy.

Common mistakes

Using inaccurate body fat estimates

FFMI depends strongly on body fat percentage, which can be hard to measure precisely.

Treating FFMI as diagnosis

FFMI is a fitness estimate, not a medical diagnosis.

Mixing height units

Imperial height should be total inches, while metric height should be centimeters.

Using it to judge natural status

FFMI alone cannot prove whether someone is natural or enhanced.

FAQs

What does this FFMI Calculator calculate?
It calculates FFMI, normalized FFMI, estimated fat-free mass, estimated fat mass, and a broad fitness category.
What does FFMI mean?
FFMI means fat-free mass index, a measure of lean mass relative to height.
What inputs do I need?
You need height, weight, and estimated body fat percentage.
What is normalized FFMI?
Normalized FFMI adjusts FFMI for height differences using a reference height.
Is FFMI better than BMI?
FFMI separates estimated lean mass from fat mass, while BMI only compares total weight to height.
Is this medical advice?
No. This calculator is for educational fitness estimates only.
Can FFMI prove someone is natural?
No. FFMI alone cannot prove natural or enhanced training status.
How accurate is FFMI?
It depends heavily on the accuracy of body fat percentage and body weight inputs.
Can women use this calculator?
Yes, but broad interpretation ranges may differ by sex and training background.
Can teenagers use this calculator?
It is intended for adult fitness estimates; younger users should avoid overinterpreting the result.
Why enter height in total inches?
A single total-inches field keeps the calculator reusable in the current engine.
What body fat method should I use?
Use the most consistent method available, such as DEXA, calipers, or the same scale over time.
What is fat-free mass?
Fat-free mass is estimated body weight minus fat mass.
Why is normalized FFMI different from FFMI?
The normalization formula adjusts the score around a reference height of 1.8 meters.
Does this calculator store my body data?
No calculator-specific body data submission is required. The calculation runs through the site calculator engine.

References

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Last updated and version history

Last updated: 2026-07-05

  • 1.0.0 (2026-07-05): Initial FFMI calculator release.