Does FFMI upload my file or text to Tool-You servers?

No. FFMI runs in this browser tab. Files stay on the device. Limit note: Weight, height, body fat %. Not medical advice.

Should I use Lean Body Mass instead of FFMI?

Use FFMI when you need Fat-free mass index from weight and body fat %. Use Lean Body Mass when you need Boer estimate from mass, height, and sex. They share a category (Health) but not the same job.

FFMI

Fat-free mass index from weight and body fat %.

Lean mass over height squared. Unlike Lean Body Mass this also prints FFMI. Unlike BMI this removes estimated fat mass first. Not medical advice.

What FFMI does

Lean mass over height squared. Unlike Lean Body Mass this also prints FFMI. Unlike BMI this removes estimated fat mass first. Not medical advice.

Practical limit for FFMI: Weight, height, body fat %. Not medical advice. That is why output can differ from heavy desktop Health software. Read the tool-specific note again: Lean mass over height squared. Unlike Lean Body Mass this also prints FFMI. Unlike BMI this removes estimated fat mass first. Not medical advice.

How to use FFMI

Confirm you need FFMI, not Lean Body Mass (Boer estimate from mass, height, and sex.). Address: /health/ffmi.
Enter the numbers or dates FFMI uses. Fat-free mass index from weight and body fat %.
Read the result as FFMI defines it — not as Fat Mass (Fat mass with lean kg.). Lean mass over height squared. Unlike Lean Body Mass this also prints FFMI. Unlike BMI this removes estimated fat mass first. Not medical advice.
FFMI is an estimate in the browser, not professional advice. Weight, height, body fat %. Not medical advice.
Need a different formula? Try Fat Mass (Fat mass with lean kg.) instead of stretching FFMI.

When not to use FFMI

Skip FFMI when a neighbor tool matches better — start with Lean Body Mass or Fat Mass — or when the description already warns the job will fail. In the tool’s own words: Lean mass over height squared. Unlike Lean Body Mass this also prints FFMI. Unlike BMI this removes estimated fat mass first. Not medical advice.

Questions about FFMI

What does FFMI do that other Health pages on this site do not?: Lean mass over height squared. Unlike Lean Body Mass this also prints FFMI. Unlike BMI this removes estimated fat mass first. Not medical advice. Short version: Fat-free mass index from weight and body fat %.
Does FFMI upload my file or text to Tool-You servers?: No. FFMI runs in this browser tab. Files stay on the device. Limit note: Weight, height, body fat %. Not medical advice.
Should I use Lean Body Mass instead of FFMI?: Use FFMI when you need Fat-free mass index from weight and body fat %. Use Lean Body Mass when you need Boer estimate from mass, height, and sex. They share a category (Health) but not the same job.
What are the limits of FFMI?: Weight, height, body fat %. Not medical advice. Also: Lean mass over height squared. Unlike Lean Body Mass this also prints FFMI. Unlike BMI this removes estimated fat mass first. Not medical advice.