Ideal Body Weight Formula: How to Calculate Your Ideal Weight
When I first meet a training, or coaching client, I normally ask, “How much would you like to change your weight?” Most of them pause, shrug their shoulders, and then reply, “I’m not sure, maybe…” then take a guess at how much weight they want to lose. The amount of weight you want to lose (or gain) doesn’t have to be a guessing game. There’s a formula to calculate your goal weight more precisely so you can have that magic number in your head that motivates you to eat well and train hard.
Old Ideal Body Weight Formula: BMI
The most common method of measuring your ideal weight is using the Body Mass Index (BMI), which measures the relationship between your weight and your height.
Do you notice anything wrong with the traditional BMI calculation, which is used in almost every weight loss study? It doesn’t take into account your body fat percentage! In fact, Ancel Keys is given credit for popularizing BMI in a 1972 paper, but he explicitly stated BMI was appropriate for population studies, NOT individual diagnoses.
Using BMI, just about every NFL football player is considered obese, even though most have very low body fat percentages. Conversely, the number of “overfat” Americans is believed to be higher than what BMI predicts. You don’t have to be overweight by the BMI Index to be considered “overfat” on a body fat basis.
So here’s a BMI calculator from the Mayo Clinic for your reference. A value between 18.5 and 25 is considered a normal weight:
BuiltLean.com Ideal Body Weight Formula
It turns out there’s a MUCH better way to calculate your ideal weight that takes into account your body fat percentage. Here it is:
Lean Body Mass/(1- Desired Body Fat Percentage)
where Lean Body Mass (LBM) = Your Body Weight – (Your Body Weight x Your Current Body Fat Percentage)
Just to be clear, your LBM is your “fat free” mass, in other words, everything in your body that’s not fat: your bones, blood, muscle, and organs.
Let me give you an example of this ideal body weight formula in action so you can see why it’s so useful. Let’s take Jake who is 200 pounds and has 22% body fat. Using this information, we know that his LBM is 156 pounds and the amount of body fat he has is 44 pounds. So what should Jake’s ideal weight be? Well that’s really up to him. For most men, a mid double digit body fat percentage of say 15% is considered pretty good. Here’s a chart for your reference:
So now, here’s the important part. We are going to assume Jake doesn’t lose any muscle because he has been following all the tips I’ve discussed so far on BuiltLean.com. So keeping his LBM at 156 pounds, Jake needs to drop 16 pounds of fat to reach his desired body fat percentage of 15%. His ideal weight is 184 pounds in this scenario. Here’s how Jake’s ideal body weight calculation looks:
156/(1-15%) = 184 pounds
See how valuable this is now? Your body weight doesn’t have to be a guessing game anymore. I’ll be following up with some articles on the various ways to calculate your body fat percentage. For now, I advise going to your local gym and having one of the trainers do a skin fold body fat measurement, or you can grab an Accu-Measure Personal Body Fat Caliper
I hope this has cleared up some confusion for you and highlighted the importance of thinking about your weight in terms of your body fat percentage.
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Although my body fat percentage is good, I don’t think I have enough muscle. Is there a guideline/equation for how much one’s muscle mass should be for a specific height, age, and gender?
That’s a good question. The guidelines I know about in terms of height/weight is the BMI, then in terms of body fat percentage is the ACE guidelines. I will write more about how to calculate body fat percentages, “ideal” body measurements, and various body fat percentages and what they mean. It’s tough to include everything in one post. Eventually, once I have written enough blog posts, I will link them together so BuiltLean.com will become a web of knowledge and a great free resource with depth and breadth.
When I look to calculate BMI I see that metric and English are reversed. It does not seem to matter though as I used pounds and inches on the metric scale and received a reasonable result. Unfortunately, I think that the scale does not really reflect people who are training. Using the Ideal formula seems more accurate but leaves me needing to knockoff 10 lbs of fat.
Hi Hank, That’s strange, I don’t have that issue when I use the BMI calculator. I’ll try to see if I can resolve the issue, but if I can’t, then just take your weight in kg and divide it by the square of your height in meters. Using imperial units, take 703 and multiply it by your weight in pounds, then divide by the square of your height in inches.
I have never seen this information anywhere. It is so interesting to be able to actually calculate body fat. This is so helpful.
Great Article!!
Thanks a lot. I appreciate it!
There’s a theoretical weight maximum that any musculoskeletal system can support without surpassing health-risking, excessive body fat.
The only way for someone to exceed the weight maximum is to pack on adipose tissue (body fat).
To calculate your weight maximum, starting from a baseline, which differs for males and for females, add or subtract weight.
For men, the baseline is 5-feet, 9-inches tall and a Maximum Weight Limit of 175 pounds. Add or subtract 5 pounds for every inch you are taller or shorter than 5 feet, 9 inches
For women, the baseline is 5-feet tall and a Maximum Weight Limit of 125 pounds. Add or subtract 4.5 pounds for each inch you are taller or shorter than 5 feet.
Your Lean Body Mass (LBM) formula amounts to overly complicated foolery.
Clearly, a man who works out regularly and stands 5’9″, 175 is going to be healthier than a man who stands the same height and weight but never works out. The same can be said for the 5′ woman weight is 125.
I see where you’re coming from. There is one more layer that I did not touch upon that relates to dividing LBM by someone’s height. So the way to arrive at the theoretical weight maximum you are referring to, is to use LBM vs. weight, come up with some type of maximum ratio, then take the highest body fat percentage acceptable (whatever that is). That’s the theoretical weight maximum. There should also be a theoretical minimum as well. I’m going to explore this in more depth in another post. I didn’t want to make this current post too long.
The LBM formula is definitely not appropriate for population studies, but I find it EXTREMELY valuable with individual clients and use it all the time. Separating LBM from fat and playing with different desired body fat percentages and how that relates to body weight is very, very useful. Also, I love how the formula allows for changes in LBM assumptions if someone gains/loses muscle to arrive at their new weight.
-Marc