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Categories: General Health

Ideal Body Weight Formula: How to Calculate Your Ideal Weight

By Marc Perry / April 18, 2018

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.

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 – 0.15) = 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 for $6 at Amazon.com and do it yourself (it’s surprisingly accurate for most people).

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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91 Comments

  • lv says:

    I'm confused with this formula.. I'm trying to get my ideal weight

    • Marc Perry, CSCS, CPT says:

      Ic - try reading over some of my answers to the comments and plug in your numbers into the equation. I hope to create a calculator at some point!

  • Lesa says:

    Thanks, Marc! I had been restricting my diet to 1200 calories a day for the last two months but was seeing very little change. I have been eating very well and tracking everything that I consume. After reading more about calorie intake, starvation mode, and considering how sluggish I sometimes felt during workouts, I have upped my calories a bit to 1400ish. It's a scary thing to do, since I'm so used to the thought of eating less to lose weight. However, the majority of the added calories is coming from a heartier breakfast and an added protein shake. I feel more energized through my workouts so hopefully this is the solution!

  • levi says:

    I need you advise please if i clculate the lmb corectly? 1,75 m high, 47 years old.

    My weight is 80 kg, my fat precantage is 25%, I would like to be in 15% fat only. the calculation is as follow:

    80-(80*0.25)= 60

    60/(1-0.15)= 70.5 the best wight, isit correct?? thanks

    • Marc Perry, CSCS, CPT says:

      @levi- Yes, the answer is 155lb, or 70 kilograms.

  • Terra says:

    I've never liked the results according to the BMI scale. I am an athletic female, I have always been one and I lift heavy weights and carry alot of muscle but according to the BMI scale, I would be considered obese. Every 3 months I have my body fat % done by a personal trainer. This is much better and puts you in a more positive frame of mind if you're someone like me. I stay around 27% body fat which is considered normal/average. I suggest to anyone that's on any kind of weight loss regime to not only weigh BUT have someone do your body fat % on a regular basis as well. You may not see results or pounds lost like you want on the scale but if you're incorporating weights into your program, you may gain muscle and lose inches of fat. I know I may only drop a few pounds sometimes but the calipers never lie! Get yourself pinched! :)

    • Marc Perry, CSCS, CPT says:

      Thanks for sharing Terra!

  • Barbara says:

    Hi Marc,

    I've been working hard since January - gym (weights, plus a little cardio) 3x weekly plus healthy eating - and have so far dropped 45lb, from 301 down to 256. The last month or so I have started introducing some high intensity intervals within the cardio, but obviously have to take it gently owing to my size. I am 5'7", 48 yo female.

    My body fat scale tells me that, give or take, I'm around 50% body fat - so around 128lb lean. Using your formula and a desired BF% of between 25-29%. Would leave me weighing somewhere in in the range 164 to 180, which seems kinda heavy. Any comments?

    Barbara

    • Marc Perry, CSCS, CPT says:

      @barbara - as you lose weight, you will also lose water as well, which is technically part of your LBM. Also, you will probably lose a little muscle (which is ok because you won't need as much muscle with a much smaller frame). The 164-180 sounds about right, but again, my guess is your LBM may decrease below 128, it will likely be around 110-115. That's my best guess. Keep up the great work!

  • amy d says:

    I enjoyed the article. I am working (dietitian)with a very fit 35 year old recreational athlete who regularly cycles 3 hours, competes in triathlons. A trainer measured her fat with 9 sites and got 24.5. She is 142 pounds, almost 5 7. She wants to look long and lean but is built muscular. wants to lose weight but burns 500-600 cal per day (wears monitor) 1300 caLs/ long rides. What would you say about a body fat goal- maybe 20-22%?

    • Marc Perry, CSCS, CPT says:

      @amy d - I think a 20-22% body fat goal make a lot of sense, maybe even leaner if she is competitive. I wrote an article about the impact of body fat on athletic performance - How To Run Faster | #1 Tip You’ve Never Heard.

  • Rachel says:

    *sigh* I get so confused. I get into raging arguments with my doctor that I absolutely have to lose 20-25lbs according to the BMI chart that she swears by.

    I weigh 180lbs (5'8", early 30's). Multiple measurements multiple times by people trained to use calipers put me at ~20% body fat. I work out hard with high-intensity circuit workouts several times a week (swinging up to 40kg kettlebells, etc.). I run, mostly trail and hill workouts, and I bike 26 miles roundtrip 2-3 times a week. I ride horses. I record meals (15-1700 calories a day) and rarely eat processed or take-out food.

    Before I was this active (5-6 years ago), I DID weigh 30lbs less. My doctor harps every time I see her that I'm unhealthy. She thinks that surely if I just work out more or longer I should be able to just lose more weight.

    Sure, I'd love to wear a smaller size. But realistically, what more can I do?

    • Marc Perry, CSCS, CPT says:

      @Rachel - As I discussed in the article, BMI is inherently a faulty framework when applied on an individual basis. If you have a large bone structure and a lot of muscle, then that's how you are built. It sounds like your doctor is essentially telling you (whether she understands it or not) to lose a bunch of muscle, which I don't think is a good idea. My opinion is be proud of the muscle you have because it's actually quite unusual for a woman of your height to have that much muscle and my guess is as you age, it will serve you well to help protect your body against degeneration in terms of functional movement.

    • Chelsea says:

      Rachel, I have a very similar problem! I am also 5'8'' and my lean body mass is 146 (calculated by multiple formulas using the skin fold method). I know that must be quite high for a woman... but then again I have always been freakishly strong, large-boned, etc... everything about me, down to my shoe size is just bigger than typical. 20% puts me around 180. *shrug*

      • Rachel says:

        @chelsea - Wish more people accepted this.. I'm so tired of being told that I just need to eat 'less' (calories, fat, etc.) and then I'll be able to wear smaller clothing sizes. But I LIKE having a body that I can trust not to fail me when I want to do things requiring strength!

        Looking forward to the next fight with my dr... ;)

      • Marc Perry, CSCS, CPT says:

        @Chelsea - Being strong and fit is a great thing for men and women. That's my take.

      • Chelsea says:

        And if I'm not wrong about this (and I don't think I am...), it really bugs me that all of my adult life I've been told over and over again my ideal weight is in the range of 145-160... that I was made to feel bad over not being able to attain an ideal that was never really healthy for me anyway...

        • Marc Perry, CSCS, CPT says:

          @Chelsea - Yes, I agree, that is unfortunate. But now you are armed with good information.

  • caroline says:

    So sorry it appears I am dense both literally and figuritively, I cannot do this maths it's the (1-24) bit? I am 5.4, 184 ilbs and 36.1 % body fat, I am 36 yrs old.
    Love this site though so very sensible and intelligent it's my new best friend for health. thanks.

    • Marc Perry, CSCS, CPT says:

      Hi Caroline, your ideal body weight assuming 25% body fat is 140lb. Your LBM is 117lb (184 - (184 -184*.336)). I need to add an ideal body fat calculator to make this easier for everyone.

  • Diana says:

    Hi Marc,
    Your formulas make good sense to me, except I'm not sure how to calculate my own ideal weight given that I am underweight and prone to muscle injury, so I am trying to gain both fat and muscle.

    I am 5'7", female, 29 y/o with 106.2 lbs body weight, and a body fat percentage of 18.3%.

    How do I know how much muscle weight to add? This will contribute to my ideal body weight and I know that after I have that calculated, I can basically say my fat percentage should go up to about 21% of my ideal body weight. Hope you can help! Thanks!

    • Marc Perry, CSCS, CPT says:

      @Diana - well you can establish a target LBM and target desired body fat percentage, then solve the equation. That's a decent starting point. You can also work backwards like getting up to 115lb and adding 50% muscle/fat, then take our your LBM and divide your new LBM by 115 to get your new body fat percentage.

  • Adam S says:

    Hi,

    I am 5'6" 180 lbs male, 24% body fat using the navy formula. According to that I should have 135 lbs lean mass, but I am bony in many areas and feel generally weak. I used to be over 210 lbs at one point, but I felt much stronger than I do now.

    And a little bit of history - is that I went from over 200 lbs to 155 lbs in a very short amount of time eating very little - 1200 or so calories and sometimes less. Afterwards I was determined to gain weight because I felt so WEAK. but I didn't do it correctly.

    An ideal body weight for my height is 146-164 which is between 10-19% body fat with my lean body mass seems to match up.

    Bu I am just worried how much I damaged my body and do I need to be still concerned with putting on more muscle or not?!

    • Marc Perry, CSCS, CPT says:

      @Adam - I think 135lb lean body mass for someone your height is actually completely normal. I'm hard-pressed to believe you would be "bony" if you lost all the fat you have to reveal your lean muscle. My guess is you would look muscular. Strength is more a matter of neuromuscular efficiency and less big muscles. What I mean is that you can get A LOT stronger without getting bigger, because your brain sends nerve impulses to your muscles, which can become more efficient and recruit more muscle fibers. Think how powerlifters can be stronger than bodybuilders double their size. I plan on writing a longer post on how to get stronger in the next couple months.

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