Measure body fat with only a gallon jug (and a couple thoussand tons of water)

Ok, so you don’t want to read the boring physics behind it all and you just want to start measuring. Fine.

Equipment

  1. gallon jug
  2. permanent marker
  3. measuring cup
  4. balloon
  5. straw or tubing
  6. spreadsheet
  7. swimming pool

Prepare the Jug

Prepare the gallon jug by pouring ½ cup water into the jug on a level surface, wait for the water line to settle, and mark it with your marker. Label this mark as 15½ cups (1 gallon minus ½ cup). Continue in this manner until the jug is filled. You might notice that the jug actually holds a little more than a gallon, don’t worry about it; just stop at 0.

Estimate RV

  1. Fill the gallon jug with water and turn it upside down in the pool, so that it remains filled with water.
  2. Hold the straw so that you can blow air into the jug.
  3. Take as deep a breath as possible.
  4. Blow up the balloon as much as you can with that breath.
  5. Blow into the straw until you have exhaled completely.
  6. Release the air from the balloon into the jug. If necessary, refill the jug with water when you reach the 0 mark.
  7. Cap the jug and set it right-side-up on a level surface. Read your vital lung capacity (VC) at the water level (add 16 cups if you had to refill the jug).
  8. Enter VC into the spreadsheet and read your estimated RV. Or, use the formula RV = VC/3.

You only need to do this once every several months.

Measure %BF

  1. Weigh yourself.
  2. Fill the jug halfway with water.
  3. Exhale completely, and Submerge yourself and the jug.
  4. Observe whether you sink, float, or neither.
  5. If you sink, pour out some water. If you float, add more water. Try again.
  6. Once you neither sink nor float, set the jug on a level surface and read the volume of the buoy.
  7. Plug your weight and buoy volume into the spreadsheet and read your density and %BF. Or, print a nomogram so that you don’t have to wait until you get back to your computer.