Body composition

Fat-Free Mass Index Calculator

FFMI normalizes lean body mass to height, like BMI for muscle. Useful for tracking lean gains independent of body fat changes.

Fat-Free Mass Index (FFMI) is your lean body mass in kilograms divided by your height in meters squared. It's a height-normalized way to track muscularity. Untrained men sit around 18–20; serious natural lifters reach 22–25.

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Your daily target

· cal/day

Enter your details and click Calculate

  • BMR · cal/day at rest
  • BMI ·  
  • Lean body mass · kg

Pick your goal

Macros at maintenance

30% protein · 40% carbs · 30% fat

Advanced metrics

Numbers are estimates. Eat at your target for 2 to 3 weeks, track weight, and adjust by ±100 cal/day if it does not match your real maintenance. See how accurate is TDEE?

Show advanced metrics 12 metrics · 7 formulas · 2D macro selector · life-stage

All metrics

Calculate above to populate the full metric table.

All 7 BMR formulas (side-by-side)

Mifflin–St Jeor · Harris–Benedict (revised) · Katch–McArdle · Cunningham · Average · Simple multiplier · Custom

TDEE across activity levels

See how much your TDEE changes between sedentary and athlete. Highlighted bar is your current selection.

Macros: 2D selector

Goal × carb-split matrix: Cut / Maintain / Bulk × Low / Moderate / High carb.

Life-stage adjustments

Luteal phase · Pregnancy (T1/T2/T3) · Breastfeeding · Perimenopause · PCOS

Typical FFMI ranges

  • Men: untrained 18–20, intermediate 20–22, advanced natural 22–25, ceiling ~26
  • Women: untrained 14–17, intermediate 17–19, advanced 19–21, ceiling ~22

FFMI requires a body fat percentage measurement. Without one, the calculator estimates lean body mass via the Boer formula.

Frequently asked questions

What does FFMI measure that BMI doesn't?
BMI uses total body weight, so it can't separate muscle gain from fat gain. FFMI uses only fat-free mass, so increases reflect muscle, not fat. It's the metric of choice for tracking long-term lean gains.
What's the natural FFMI ceiling?
Roughly 25 for men and 22 for women without performance-enhancing drugs, based on research by Kouri, Pope, and Lukas (1995) analyzing pre-steroid-era bodybuilders. Anyone reporting natural FFMI above 26 is statistically very rare.
How accurate does my body fat need to be?
A ±3% error in body fat translates to ±2 kg in lean mass, which is meaningful at the high end. DEXA or hydrostatic methods give the cleanest FFMI estimates.