The formula for density is--Density =Mass/volume. To find the mass of an object, it can be weighed using a balance or a digital scale. The units will be in grams. To find the volume of that object, if it is floating, you need to find out how much water the object displaces. Therefore, you need a graduated cylinder with a known quantity of water. Next, drop the object into the cylinder and the water level will rise to a new volume. Subtract the two numbers and this will give you the volume of the object. Using the density formula, plug in the mass in grams divided by the volume in mililiters. If the object floats in water, its density will be less than 1 gram per mililiter. Ice is a solid that can float in water, because water expands as it cools making it less dense than liquid water. Liquid water has its greatest density at 4 degrees Celsius. Other solids that can float in liquid water include stryofoam, wood and some clothing.
You can find out the mass of the solid using a weighing scale. Since you need to find the mass and volume to find the density, you will need to find the volume of the solid. Now you will need two set-ups. In the first setup you will have a measuring cylinder with some water. Using a string, tie a weight or anything else to the solid so that it is fully submerged in the water. Record the volume. For the second set-up, you will have an identical measuring cylinder with the same amount of water. Place the weight that you used to weigh down the solid earlier. Record the volume. Use the volume recorded in the first setup and subtract the volume recorded in the second setup. The answer is the volume of the solid.
Hope this helps.