Body Fat Calculator

How to Calculate Your Bodyfat Percentage

Click here for a nice online calculator

Hugo Rivera, writes, "One thing we engineers love are formulas and these I have found to be pretty accurate to calculate bodyfat. They are within +/- 3% of the real value. All you will need is a tape measure, a piece of paper, pencil or pen and a calculator."

A common response in our forum is that this is too complicated. Many of us estimate progress by the mirror, the belt or the tightness of the button on the jeans.

Here's a lean body mass calculator from the National Institute of Health.

Meanwhile, Hugo offers up the following formula:

Click here to use the formula in an Excel spreadsheet
(You'll need the formula notes below for measurement descriptions)

For Men:
Before you use the formulas, there are two measurements that are required:

Measurement 1: Bodyweight

Measurement 2: Waist Girth (measured at the umbilicus)

1) Multiply your bodyweight by 1.082. Add the result to 94.42. Once your calculation is complete, save the number. à (Bodyweight x 1.082) + 94.42=Result 1

2) Multiply your waist girth by 4.15. Once you get this result, subtract it from the number obtained in step 1 (ie: Step 1 result-Step 2 result). The result obtained after the subtraction is done is your lean bodyweight (your weight if you had no fat in your body at all). à Result 1 - (Waist Girth x 4.15)= Lean Body Weight

3) Finally, subtract your lean bodyweight from your total bodyweight (Total weight-Lean Bodyweight). Once you get the result, multiply that number by 100. Once you get the result divide it by your total bodyweight. This final result is your percentage of body fat. à ((Total Bodyweight - Lean Bodyweight) x 100) divided by (Your Body Weight) = Your Percentage of Body Fat.

I weigh 190 and I have a 30.5inch waist. Therefore, step 1 is (190 x 1.082) + 94.42 = 300. Step 2 says that my lean body weight equals 300-(30.5 x 4.15)=173.425. Finally, Step 3 says that my body fat percentage is ((190-173.425) x 100) divided by 190= 8.72%.

For Women:
Before you use the formulas, there are five measurements that are required (not fair, I know):

Measurement 1: Bodyweight.

Measurement 2: Wrist Circumference (measured at the widest point).

Measurement 3: Waist Circumference (measured at your umbilicus).

Measurement 4: Hip Circumference (measured at the widest point).

Measurement 5: Forearm Circumference (measured at the widest point).

1) Multiply your bodyweight by 0.732. à Bodyweight x .0732 = Result 1.

2) Add the result above to 8.987. à Result 1 + 8.987= Result 2.

3) Divide your wrist circumference by 3.14. à Wrist divided by 3.14 = Result 3.

4) Multiply your waist measurement by 0.157. à Waist x 0.157 = Result 4.

5) Multiply your hip measurement by 0.249. à Hip x 0.249 = Result 5.

6) Multiply your forearm measurement by 0.434. à Forearm x 0.434 = Result 6.

7) Add results 2 & 3. à Result 2 + Result 3 = Result 7.

8) Subtract Result 4 from Result 7. à Result 7 - Result 4 = Result 8.

9) Subtract Result 5 from Result 8. à Result 8 - Result 5 = Result 9.

10) Add Result 6 and Result 9. The result is your lean body mass (your fat free weight) à Result 6 + Result 9 = Lean Body Mass.

11) Subtract your lean body mass from your bodyweight. Once you get the result, multiply that number by 100. Once you get this result, divide it by your bodyweight. à ((Bodyweight-Lean Body Mass) x 100) divided by your bodyweight.

A woman that weighs 125, and has a wrist measurement of 6.0, a waist measurement of 24, a hip measurement of 38, and a forearm measurement of 9.5 would calculate her body fat percentage in the following manner. Step 1: 125 x 0.732=91.5. Step 2: 91.5 + 8.987=100.487. Step 3: 6 divided by 3.14=1.91. Step 4: 24 x 0.157=3.768. Step 5: 38 x 0.249=9.462. Step 6: 9.5 x 0.434=4.123. Step 7: 100.487+1.91=102.397. Step 8: 102.397-3.768=98.629. Step 9: 98.629-9.462=89.167. Step 10: 4.123+89.167=93.29 (Lean Body Weight: Fat Free Weight). Step 11: ((125-93.29) x 100) divided by 125 = (31.37 x 100) divided by 125 = 3171 divided by 125= 25.368 (Body Fat Percentage).


Notes: The formulas above are just approximations. The goal here is to have a point of reference from which to work. I recommend that you measure your body fat every three weeks. If you see a pattern where you see yourself gaining muscle and losing fat, then you know your program is right on track. If not, examine which part of your program is not optimal. Assuming that you are following an effective training routine, look at the things that could be going wrong such as you are not getting enough rest at night or more likely you are not following your nutrition plan to the letter.

Since I like to measure my progress, and that of others, in the shortest amount of time possible, I created a computer program that once you enter the required inputs, it calculates in a microsecond your lean body mass, fat mass, and body fat percentage. It sure beats using the calculator, the pen or pencil and the piece of paper.

Have fun!
Hugo Rivera

Click below for more:

Fabulous book on habit change with fat-loss workouts by Josh Hillis & Dan John:
Fat Loss Happens on Monday

To use our online bodyfat calculator

To use the formula in an Excel spreadsheet

To read the IronOnline Forum Archive

Go back to the 8-Week On Target Workouts

Click here for sample workout routines

May we answer any questions for you in our forum?

If you haven't yet read Dave's bodybuilding book, Brother Iron, Sister Steel, click here for more information.