Backed by sports-science formulas
TDEE, FFMI, Macro & 1RM Calculators
Instant, science-backed fitness math: TDEE (Mifflin-St Jeor), FFMI, daily macros, and one-rep-max — mobile-first, ad-light, 100% free.
FFMI & Normalized FFMI
Measure lean-mass quality independent of body fat.
Your Result
- < 18 · Below average
- 18 – 20 · Average
- 20 – 22 · Advanced natural
- 22 – 25 · Genetic limit
- > 25 · Exceptional / likely enhanced
Body Fat % — US Navy Method
A tape measure is all you need. ±3–4% accuracy vs DEXA.
Your Result
Body Fat Categories
| Category | Men | Women |
|---|---|---|
| Essential fat | 2–5% | 10–13% |
| Athletes | 6–13% | 14–20% |
| Fitness | 14–17% | 21–24% |
| Average | 18–24% | 25–31% |
| Obese | 25%+ | 32%+ |
Lean Body Mass
The weight your body carries minus fat — muscle, bone, organs, water.
Your Result
Why it matters: Lean mass is the main input for FFMI. Tracking it over time is a cleaner progress signal than scale weight — you can be losing fat and holding lean mass without the scale moving much.
TDEE & BMR
Mifflin-St Jeor — the gold-standard predictive BMR equation.
Daily Energy
Goal Targets
Macro Distribution Matrix
Pulls your TDEE result and splits it into Protein / Carbs / Fats.
Your Daily Plate
| Macro | % | kcal | grams |
|---|---|---|---|
| Protein | — | — | — |
| Carbohydrates | — | — | — |
| Fats | — | — | — |
Protein & Carbs = 4 kcal/g · Fats = 9 kcal/g
1RM Calculator
Estimate your one-rep max with Epley & Brzycki — plus a full %1RM table.
Your Estimated Max
% of 1RM Reference
| Reps | % 1RM | Weight |
|---|
Frequently Asked Questions
Plain-language answers grounded in peer-reviewed sports science.
What does FFMI actually measure?
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FFMI = Lean Mass (kg) / Height (m)².
Where does the 25 FFMI "natural limit" come from?
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Why normalize FFMI?
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FFMI + 6.1 × (1.8 − Height m) so comparisons across body sizes are fair.
How accurate is the Mifflin-St Jeor TDEE estimate?
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Which 1RM formula should I trust?
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w × (1 + reps/30)) and Brzycki (w × 36 / (37 − reps)) perform best at ≤10 reps. Use the average for planning, and always validate with a true heavy single under supervision.
From the FFMI Check Journal
Deep dives on body composition, programming, and the science behind the numbers.
About FFMI Check
FFMI Check was built by a small group of lifters who got tired of bouncing between half-broken calculators, paywalled apps, and influencer-driven fitness blogs that prioritized newsletter sign-ups over actual science. We wanted one clean place where any athlete in the world could measure what truly matters — lean mass, energy needs, macros, and strength — in under 30 seconds, for free.
Our mission is simple: turn peer-reviewed sports science into instant, beautiful, mobile-first tools. Every formula on this site — Mifflin-St Jeor, Kouri's normalized FFMI, Epley, Brzycki — is implemented exactly as published, with the citations available in plain sight. No proprietary "secret sauce." No upsells.
What we stand for
- Built by lifters, for lifters. Every feature is something we wanted ourselves.
- Science-first. If a formula isn't peer-reviewed, it isn't on this site.
- Free forever. Supported by lightweight, non-intrusive advertising — never by selling your data.
- Open in spirit. Our formulas, classifications, and methodology are documented on every page.
Partnerships, Press & Feedback
We read every message. Whether you found a bug, want to advertise, or have a research partnership in mind — drop us a line.
The FFMI Check Blog
Long-form, peer-reviewed-grounded reads to help you turn raw numbers into smarter training decisions.
- Beyond BMI: Why FFMI is the Only Metric That Matters for Lifters — Body Composition · 7 min read — Why the body-mass index fails athletes — and how lean-mass-driven metrics replace it for serious training decisions.
- The Natural Limit: Understanding the Science Behind the 25 FFMI Ceiling — Sports Science · 9 min read — A deep dive into the 1995 Kouri study, the golden-era physiques that hinted at it decades earlier, and why height normalization matters.
- The Athlete's Guide to Estimating Body Fat Percentage Safely at Home — Practical Guide · 10 min read — Garbage in, garbage out. Your FFMI is only as accurate as your body fat input — here is how to get it right without leaving your bathroom.
- Mifflin-St Jeor TDEE Calculator: How Accurate Is It, Really? — Energy Balance · 8 min read — The Mifflin-St Jeor equation is the most-cited TDEE formula on the web — but how close does it actually land to a metabolic cart? Inside the data.
- TDEE Calculator to Lose Weight: The 4-Step Setup That Actually Works — Fat Loss · 9 min read — A TDEE number alone will not melt fat. Here is the four-step protocol that turns a calculator output into a calibrated, sustainable cut.
- Epley vs Brzycki: Which 1RM Formula Should You Actually Trust? — Strength · 7 min read — Two formulas, two slightly different answers. Here is when each one wins, when both fail, and how to combine them into the safest estimate.
- What Is a Good FFMI? Benchmarks by Age, Height & Training Years — Body Composition · 8 min read — A "good" FFMI depends entirely on your training age, height, and biological sex. Here are the realistic benchmarks lifters actually hit at each stage.
- Average FFMI by Age & Height: The Realistic Benchmark Table — Body Composition · 9 min read — Where should your FFMI actually land for your age and height? Data-backed benchmarks so you can stop comparing yourself to teenagers on Reddit.
- Golden-Era Bodybuilders FFMI: A Reference Guide to Pre-Steroid Muscularity — History & Reference · 12 min read — Where did the "FFMI 25 natural ceiling" come from? A ground-truth reference of drug-free bodybuilding legends, their measurements, and the science that made 25 the accepted natural limit.
- Macro Calculator for Muscle Gain: The Numbers That Actually Move Lean Mass — Nutrition · 10 min read — The macro split for muscle gain is not a mystery. Get protein, calories, and split right, and lean mass moves. Here is the actual math and how to adjust as it stops working.