The swell and shrink factors are based on the material in its original state. If you combine the two factors you get a factor (Spike's compaction factor) which will convert loose state volume to compacted volume of the material. You can use this factor to estimate the amount of material you need to bring in for a certain area that needs to be compacted.

You need to backfill and compact an area of 200 ft long by 20 feet wide with a depth of 8 feet.

200*20*8 = 32000 cubic feet

Convert to cubic yards:

32000/27 = 1185 cubic yards

Assume you are using dry gravel with a swell percentage of 15% and a shrink percentage of -7%

Plug those values in to the calculator and it will tell you that the compaction factor = 1.273.

Multiply the 1185 cubic yards by 1.273

1185 * 1.273 = 1508.

To complete this job you will need 1508 cubic yards of this gravel in loose state volume.

The Spike's Compaction Factor can also be used to estimate the amount of material you need to purchase for an area that needs to be filled and compacted. For instance you need to place a 6" layer of gravel inside a foundation. Your calculation of the area for a 20' x 20' wide with a depth of 6" would give you a volume needed of 20 * 20 * .5 = 200 cubic feet.

From the first example the compaction factor = 1.273 based on 15% swell and -7% shrink for this material.

Convert 200 cubic feet to cubic yards = 200/27 = 7.4 cubic yards

7.4 cubic yards * 1.273 = 9.4 cubic yards.

This 9.4 cubic yards can then be used as an "ESTIMATED" amount of material needed for this job. And that is an "ESTIMATED Amount"!