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.
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
Some good points here. Will add this to my rss reader.
@ Fat Loss Guy – Thanks a lot for the kind words. I just realized the RSS reader is not working for some reason, so I’ll make sure that I can get that fixed up and let you know!
How did you manage to make a blog thats as smart as it is sleek? I mean, its like an Aston Martin –smart and sexy at the same time.
I really enjoy when people are indicating their judgment and idea. And so I prefer the way you are producing.
But how does your skeletal makeup reflect in all this? It seems Ketch Rudder’s baseline post seems overly simplistic, especially for the skeletal makeup. I’m no expert, just an ordinary person with a question and thought. I’m 5′ 1″ and female. Some women at my height have sparrow like bone structure, whereas, I have a much thicker bone structure. The sparrow can look perfectly fine at 100 lbs or even less. I look and feel awful at less than about 115 and actually feel healthiest at around 125. Wouldn’t the max weight on a sparrow skeleton be less than a heavier skeleton?
@Connie – Thanks for the comment. I’m not familiar with “Ketch Rudder”, but I do understand your valid point that different people have different bone structures and therefore LBM’s. As you say, someone who has a thinner bone structure should weigh less than someone at the same height with a thicker bone structure. In the formula I propose, it’s dependent on your body fat percentage so if you have a high LBM, that’s totally fine. With the BMI, a large bone structure will probably indicate overweight/obesity. The BMI can be helpful when looking at population statistics, but not on an individual basis. That’s really the point I was trying to make.
Hi Marc.
I recently found out that my LBM is about 97 lbs. and I’m 119 lbs. Is this a good number? My body fat is 17% and my BMI is 19.2 so those numbers are good (I’m told). Also, I’m 5’6″tall. Do I need to build more muscle or just maintain at this point? I’d love to lower my body fat percentage to like 15-16% but other than that I’m pretty satisfied with the way I currently look at this point. What do you think? I’d love to get your expert opinion. Thanks.
This formula works much better for me than the BMI or the one “Ketch Rudder” came up with.
For me (5′ 10″) to make it into Ketch’s formula I’d have to maintain a BF% of less than 5. At 5′ 10″ I weight in at 195 and have just about 10%. His formula says that anything over 180 lbs is unhealthy for me. That simply cannot be right.
That formula is much to simple to take into account all the varying skeletal sizes that people of the same height have. I have a friend who is my height and is much less “broad”. I have very broad frame (think defensive lineman).
So this one you made up here is much more accurate per person. The BFFM diet also uses this formula and it’s very nifty.
@Ian – Happy you liked the article. BFFM is a solid book and Venuto is a VERY knowledgeable guy.
Generally BMI is used in athletics to divide athletes into various groups. This is the best to know your fitness level.
Hello Marc, I’m 5’8 138 pounds and 23 years old. I’m on the skinny side and according to my BIA scale I’m around 12 percent body fat, not sure how accurate that is though. My goal is to reach 7-8 percent body fat, but my goal as is how much to actually weigh is where I get lost and confused. I know I need to gain weight and build muscle, but I just don’t know how much weight or muscle I should actually gain. I absolutely do not want a bodybuilders physique. My goal is to achieve a lean and muscular physique that of a fashion model, decent amount of muscle with low body fat. Any suggestions on how I can attain my goal? How much muscle or weight I should gain? thanks for any help and great website.
@Randy – My suggestion would be to lose a little more body fat (let’s say a 5 pounds) without losing muscle and see if you are happy. right now your LBM is 121lb, so if you lose 5lb of muscle while keeping your LBM the same, your body fat will be around 8%. If you are not satisfied with how big you are, then you can add some muscle while being careful not to add to much fat. Check this out for more information on Ideal Weight.
Thanks Marc, and what is your suggestion on how much muscle is a decent amount of muscle to gain? 10 pounds, 15 pounds, or 20 pounds of muscle?
@Randy – It really depends on your goals. Everyone is different. Gaining 20lb for me would simply be way too much in my opinion. My body wouldn’t feel great with that much more muscle. It’s hard to say what 10lb of muscle will look like in the right places on your body. You may be really happy with 5lb, or 10lb, or maybe it’s not enough. I do think 10lb is definitely a solid amount of muscle to add to your frame.
This article didn’t say how much your minimum fat weight should be or can be, mine is 16.96 is it unhealthy to go lower?
@Nefaruru – What is your total weight/height? I am unable to answer your question without knowing more information.
I am 5 feet 5 inches and I weigh 105 pounds~ I have a scale that measures body fat percentage and it says 15-16% (depending on the day)
@Nefaruru – The body fat percentage, not the total amount of fat in pounds is what’s most relevant. 16lb sounds sounds fine given you only weigh 105lb. Also keep in mind the BIA scales are notoriously inaccurate. If you can, see if you can find a competent trainer to take your body fat percentage. Hope that helpful!
Thanks!
Your article is so so helpful. I was always wondering what really was my ideal weight because im 5ft8 with a weight of 194 lbs and body fat of 32% but i really dont look obese as my BMI would say but more like a curvy woman with an hourglass shape, its always strange when people know how mu ch i weigh they are always surprised and tend to say i may have heavy bones so i dont know if thats d case, anyway now i know i need to be at 160 lbs to have a 20% body fat, so that i can finally see some definition on my stomach…so thank u, i now have a goal
@cythnia S – Very happy you enjoyed the article and found it useful!
Hello! Thanks for having this helpful site. I just had a baby
I am completely uncomfortable with my body, weight n health overall. I am 33 stand at 5’4 and 180 lbs!! My body fat is 41.2 
What should my ideal weight and body fat? Help
@Aylissa – Congrats on your baby! That’s great news. I haven’t met too many women who feel slim and sexy after having a baby (i.e. I haven’t met any), so my guess is the emotions you are feeling regarding your body weight are quite common. With that said, I do think a focus on losing 0.5-1.5lb of fat per week like clockwork could be a great goal for you. My guess is a healthier body weight per BMI standards would be closer to 140lb. Body fat would be around 24%.