Enter the dry soil weight (g) and the soil volume (cm^3) into the calculator to determine the bulk density of the soil.
Bulk Density Formula
The following formula is used to calculate the bulk density of soil.
BD = DSW / SV
- Where BD is the bulk density (g/cm^3)
- DSW is the dry soil weight (g)
- SV is the soil volume (cm^3)
Bulk Density Definition
What is bulk density? A bulk density is the total weight of dry soil per unit of volume. In other words, the density of a soil without any water in the soil.
How to calculate bulk density?
- First, determine the soil volume.
For this example, a sample of soil is taken with a hollow cylinder that has a height of 20cm and a diameter of 5cm. Using the formula for volume of a cylinder, we find the volume to be V = pi*h*r^2 = 3.14159*20*(5/2)^2 = 392.698 cm^3.
- Next, determine the dry soil weight.
To determine the soil weight, first, we weigh an empty container. This is found to be 10 grams. Next, we microwave the soil to remove all water and weigh it again on the container. It comes out to 130 grams. Finally, we determine the dry weight by subtracting the container weight from the soil weight. 130-10 = 120 grams.
- Finally, calculate the bulk density.
Using the formula above, we can calculate the bulk density. BD = 120/392.698 = 0.305 g/cm^3.
About Bulk Density
Are bulk density and specific gravity the same? A bulk density and specific gravity are not the same. A bulk density is a ratio of mass to volume of soil. Specific gravity is a ratio of the density of a specific object to the density of a common substance, which usually is water.
Why does bulk density increase with depth? As depth increases, the pressure acting on soil and the surrounding area increases. As the pressure increases the soil is compacted into a smaller area. This causes the bulk density to increase as depth increases.
Is bulk density the same as dry density? The terms bulk density and dry density are often used interchangeably.