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
- gallon jug
- permanent marker
- measuring cup
- balloon
- straw or tubing
- spreadsheet
- 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
- Fill the gallon jug with water and turn it upside down in the pool, so that it remains filled with water.
- Hold the straw so that you can blow air into the jug.
- Take as deep a breath as possible.
- Blow up the balloon as much as you can with that breath.
- Blow into the straw until you have exhaled completely.
- Release the air from the balloon into the jug. If necessary, refill the jug with water when you reach the 0 mark.
- 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).
- 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
- Weigh yourself.
- Fill the jug halfway with water.
- Exhale completely, and Submerge yourself and the jug.
- Observe whether you sink, float, or neither.
- If you sink, pour out some water. If you float, add more water. Try again.
- Once you neither sink nor float, set the jug on a level surface and read the volume of the buoy.
- 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.