Health Tools

Fat Mass Index Calculator

Estimate fat mass index from fat mass and height, or from body weight and body fat percentage.

Updated April 16, 2026
Free online tool
Planning and research use

Why this page exists

Body-composition comparisons are easier to interpret when fat mass is related to height instead of being read only as a raw weight number. This calculator helps visitors estimate fat mass index from height and fat mass directly, or from height, body weight, and body fat percentage when fat mass has not already been estimated elsewhere.

Interactive tool

Run the estimate

Enter your numbers and read the result first, then use the sections below to understand what affects the outcome.

Calculator

Fat mass index calculator

Estimate fat mass index from height and fat mass directly, or from height, body weight, and body fat percentage.

Result

5.69

Estimated fat mass index based on height and either fat mass directly or weight and body fat percentage.

Fat mass index5.69

Fat mass used16.96 kg

Height used1.727 m

Reference noteGeneral body-composition estimate only

16.96 kg of fat mass at 1.727 meters tall gives a fat mass index near 5.69.
In body-fat mode, fat mass is estimated from body weight multiplied by the body fat percentage entered.
Use the output as a quick comparison-oriented body-composition estimate, not as a medical diagnosis or a complete health assessment.

This is a general body-composition estimate, not medical advice. Fat mass index can be useful for screening and comparison, but it does not replace professional assessment of body composition or health.

Planning note

Last updated April 16, 2026. Use this tool to compare scenarios and plan ahead, then confirm important details with the lender, employer, insurer, contractor, or other qualified provider involved in the final decision.

How it works

What the calculator is doing

Choose whether to start from fat mass directly or from body weight and body fat percentage.

Enter height in imperial or metric units and the other measurements required for the mode selected.

The calculator estimates fat mass if needed and divides it by height in meters squared to estimate fat mass index.

Understanding your result

Browse more health tools

Examples

Ways people use this tool

Example scenarios help turn a quick estimate into a more useful comparison or planning step.

Estimate FMI from known fat mass

Direct fat-mass input is useful when fat mass has already been estimated elsewhere and you only want the height-adjusted index.

Use body weight and body fat percentage instead

If direct fat mass is not known, body weight and body fat percentage can be used to estimate it first.

Pair it with other body-composition tools

FMI often makes more sense when viewed beside BMI, body-fat percentage, and lean-mass estimates.

FAQ

Common questions

How is fat mass index calculated here?

The calculator estimates or uses fat mass in kilograms and divides it by height in meters squared to estimate FMI.

Why offer two input modes?

Some people know fat mass directly from another estimate, while others only have body weight and body fat percentage available.

Is FMI a diagnosis?

No. It is a general body-composition estimate for planning and comparison, not a diagnosis or a substitute for medical assessment.

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Health ToolsUpdated April 13, 2026