how can you measure the density of your own body?

Answer 1

True that you need to measure your volume and your weight (or mass). But you don't need a graduated vessel to measure your volume. You can use any vessel you can fit into. You get in the vessel and fill to the top (or a reference point above the highest part of your body). Then get our of the vessel, and measure how much fluid is needed to get the level back up to the reference mark.
You could do this in a bathtub with the help of a friend. As you completely immerse yourself in the water (and hold your breath), the friend can mark the level of the water. Then get out, and using a measured container, refill the tub up to the reference mark, keeping track of how much water you put in. Add up the amount of water you put in to find out the volume of your body.

To get your mass: weigh yourself and divide by the gravitational constant.

Your density is your mass per unit volume:
(Mass/Volume)

Answer 2

You can use the Archimedean Principle. Get into fresh water such as a swimming pool (naked for the most accurate results) and measure the displacement of the water while you're floating, then hold yourself entirely underwater and measure the displacement of the water again and divide the former value by the latter value. Note that this only works if you are less dense than water, but I'm pretty sure people are less dense than water because their lungs are full of air.

Answer 3

That's kind of difficult. But you would need to find out your volume.
You can do this with a huge graduated tub. You fill it to a certain level with water then completely submerge yourself in it, and measure the difference in the water level from when you're in it and when you're not in it.
That will be your volume.
Then you weigh yourself.
Then you divide your weight by your volume.

Answer 4

A little easier method:
Weigh yourself→ Wa
Submerge yourself and weigh again (with help from an assistant and spring scale) → Ws

Specific Gravity = Wa/(Wa-Ws)

Density = 1000kg/m³ * (Specific Gravity)