The world's only FFMI calculator for gym nerds
Determine your Fat Free Mass Index (FFMI) or work backwards from your goal FFMI to find your target muscle gain / fat loss.
*You can work backwards from your goal FFMI to find the amount of muscle (lean mass) gain and/or fat loss needed to reach it.
Frequently asked questions
What is FFMI?
FFMI (Fat Free Mass Index) is a number that can tell you how muscular you are for your height. Though strictly speaking, it doesn't measure just muscle. It actually takes into account your entire fat-free mass — which includes the weight of your bones, organs, blood, and basically everything else in your body that isn't fat. But since it's a lot easier to train and grow your muscles than it is to grow your bones and organs, fitness enthusiasts very often use FFMI as a reliable way to judge muscularity. Generally, unless you’re a child and still growing, there's no natural way to grow your bones or organs. Hence, an increase in FFMI means a direct increase in pure muscle mass. It’s also important to understand that taller people will naturally have higher fat-free mass due to their taller frame. Longer limbs means longer length muscles sitting on them. That's exactly why FFMI factors in height. If you just looked at total fat-free mass on its own, a tall person would almost always be considered more “muscular" than a short person on paper — even if the short person actually has relatively better muscular development for their height. By adjusting for height, FFMI gives you a personalised score relative to your height.
What is Normalised FFMI?
Normalized FFMI gives you what your standard FFMI would have been if you were 180cm (around 5’11”). If you’re already that height, then your standard and normalized FFMI will always be the same. This makes it easier to compare two people of different heights and determine who is more muscular. This is done because taller people typically tend to have a higher FFMI than shorter people, but not necessarily because they’re more muscular. But by scaling two people’s FFMI to a reference height of 180cm, both people can easily compare muscularity without any height bias.
What is Lean Mass?
Lean mass is everything in your body that isn't fat — your muscle, bone, organs, and water. It matters because when people talk about gaining size or getting stronger, this is the part they actually mean. Separating it out from fat lets you track real muscle progress instead of being misled by changes on the scale, which lump muscle and fat together.
What is Body Fat Mass?
Body fat mass is the actual weight of the fat your body is carrying, as opposed to a percentage. A percentage alone can be hard to act on, but knowing the real amount of fat tells you concretely how much you'd aim to lose, and pairs with lean mass to show exactly what your bodyweight is made of.