THE BODY COMPOSITION WORKBENCH / CALCFFMI

FFMI Calculator for people who train with purpose.

See your estimated fat-free mass index, understand the measurement, and connect your numbers to thoughtful strength training and nutrition. One clean starting point—without the clutter.

Use the FFMI calculator ↗Browse tools ↗

METRIC + IMPERIALQuick comparison with transparent formulasNO FITNESS SHORTCUTSReference estimates, not medical judgments

01 / CALCULATE FFMIIN-BROWSER

Body weight (kg)Height (cm) Body weight (lb)Height (feet)Extra inches Estimated body-fat percentage (%)

Use a consistent body-fat estimation method. Results are estimates from the numbers entered and are not medical advice; if you have a health condition, are pregnant or have a history of eating disorders, speak to a doctor or registered dietitian.

Estimated FFMI20.99

Normalized FFMI20.99

Fat-free mass68.0 kg

BMI24.69

Calculated using your entered measurements.

Need help? Understand the formula or estimate body fat.

MEASUREUNDERSTANDPLANREASSESS

01 / YOUR BASELINE

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Better fitness decisions begin with better measurements.

A single scale reading cannot tell you how much of your body is fat, muscle, bone or water. FFMI adds another perspective by relating estimated fat-free mass to height. It is useful for tracking direction, not for declaring who is healthy, who is elite or who is using performance-enhancing drugs.

If you are new to the concept, start with What Is FFMI? and then see How to Calculate FFMI. Your body-fat input matters: a change in measurement method can shift FFMI even when your actual physique has not changed. The How to Measure Body Fat explains practical measurement choices, while the Body Composition Guide covers the differences between fat mass, lean mass and total weight.

THE CORE IDEAFat-free mass (kg) = body weight × (1 − body-fat fraction)FFMI = fat-free mass (kg) ÷ height² (m²)Normalized FFMI in the original Kouri study: FFMI + 6.3 × (1.80 − height in metres). This is a comparison adjustment, not a medical diagnosis.

For example, a person at 80 kg, 1.80 m tall and 15% estimated body fat has about 68 kg of fat-free mass and an FFMI of approximately 21.0. If the same person estimates body fat at 18%, FFMI drops even without a change in scale weight. That is why consistency and honest uncertainty are more useful than a single decimal place. Explore Normalized FFMI Explained for the height adjustment and FFMI Score Interpretation for measured-score context.

04 / THE TRAINING SYSTEM

Numbers help. Your next session matters more.

A calculator is useful only when it informs a decision you can repeat. Effective resistance training does not require a complicated spreadsheet: progressive sessions, appropriate load and volume, and recovery usually matter more than constantly changing methods.

The updated 2026 ACSM resistance-training guidance emphasizes consistent training and individualizing load and volume to the goal. For a starting structure, explore the Beginner Program; for greater experience, compare Upper/Lower Split with Push/Pull/Legs Split. Improve your technique and exercise selection with Compound Exercises and Progressive Overload Guide.

Explore training programs ↗

06 / WORKED EXAMPLES

What the numbers look like in practice.

Illustrative scenarios, not reference standards for individual health.

EXAMPLE A

Estimate your FFMI

Body weight: 80 kg
Height: 1.80 m
Body fat: 15%
Lean mass estimate: 68 kg

FFMI ≈ 21.0

68 ÷ (1.80 × 1.80) = 20.99. The original height adjustment is zero at 1.80 m.

EXAMPLE B

Compare measurements

Body weight: 80 kg
Height: 1.80 m
Body fat assumption: 18%
Lean mass estimate: 65.6 kg

FFMI ≈ 20.2

65.6 ÷ 3.24 = 20.25. Body-fat estimation error can affect your FFMI even if body weight stays unchanged.

EXAMPLE C

Estimate one-rep max

Lifted load: 70 kg
Completed reps: 8
Formula: Epley
Calculation: 70 × (1 + 8/30)

1RM ≈ 88.7 kg

An estimated training reference—not a substitute for good technique or a supervised maximal attempt.

PUBLISHED TOOL LIBRARY

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A SECOND QUICK TOOL

Estimate your one-rep max before your next block.

Enter a submaximal lift and completed reps for an Epley estimate. Use it as a rough reference for planning—not an instruction to attempt a maximal lift. Compare your result with the full One Rep Max Calculator, or read the Strength Standards guide for context.

Weight lifted (kg)Completed reps (1–12)

88.7 kg estimated using Epley

MORE CALCULATORS

More calculator collections.

Specialised calculators grouped by topic, with four popular tools from each collection.

Body Measurement & Fat Estimates Hub

Track waist, circumference and practical changes with consistent measurement methods.

FFMI Targets & Scenarios Hub

Model changes in lean mass, estimated FFMI and body-fat assumptions.

Strength & Barbell Calculators Hub

Plan barbell loading and understand strength training intensity.

Hypertrophy & Program Planning Hub

Organize sessions, weekly sets, training frequency and productive volume.

Calorie & Macro Planning Hub

Build calorie and macro estimates around a concrete nutrition goal.

Meal Tracking & Food Preparation Hub

Turn portion and food preparation estimates into daily planning.

Weight Trends & Composition Progress Hub

Focused tools to support more detailed fitness planning.

Cardio & Conditioning Tools Hub

Compare heart-rate zones, pacing and conditioning sessions.

Recovery, Sleep & Hydration Hub

Fitness Planning & Equipment Hub

07 / METHOD & LIMITS

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Transparent calculations. Useful limitations.

FFMI has a published mathematical definition, but its inputs may be estimated using imperfect measurement methods. The original Kouri et al. study introduced a height correction for comparing a sample of athletes. Its often-cited threshold of 25 came from a particular sample and is not a definitive test for drug use or a ceiling for every human body.

We show conventional FFMI alongside its height-adjusted version so you can see how the two differ. Interpret them with context such as training history, body-fat estimation method and height. The Natural FFMI Limit and FFMI Natural vs Enhanced pages provide an appropriate place to examine these limitations. For context by sex and sport, see [Men vs Women FFMI] and [FFMI by Sport].

Research and editorial references

Kouri et al. (1995), Fat-free mass index in users and nonusers of anabolic-androgenic steroids ↗

ACSM (2026), Resistance training prescription: overview of reviews ↗

08 / COMMON QUESTIONS

Questions worth answering.

Short explanations before you use a number to make a decision.

What is the difference between FFMI and BMI?

BMI uses total weight divided by height squared. FFMI substitutes estimated fat-free mass for total body weight, so it adds a body-composition perspective but also inherits measurement error from the body-fat estimate. See FFMI vs BMI.

Does an FFMI above 25 prove someone is using performance-enhancing drugs?

No. The value is often discussed because it appeared in a particular research sample, but it is not a reliable individual test for drug use. Body-fat error, height differences, selection effects and individual variation matter. See FFMI Natural vs Enhanced.

What measurements do I need for the FFMI calculator?

Enter your body weight, height and estimated body-fat percentage. You can switch between metric and imperial units in the quick calculator. Use consistent methods when comparing past results.

Why does normalized FFMI differ from regular FFMI?

Normalized FFMI applies a height correction from the original Kouri research formula. It adjusts the number relative to a 1.80-m reference height and is mainly used for comparison within that context. It does not make the underlying body-fat estimate more accurate.

Can FFMI tell me how much muscle I will gain?

No. FFMI can help summarize a measured baseline, but it cannot reliably predict future muscle gain or an individual's genetic ceiling. Training history, consistency, energy balance and other factors matter. Use Muscle Building Basics to build realistic expectations.

For additional topics, visit the full FAQ library.