A retaining wall should have the power to hold back the weight of the soil, plants and at times small structures behind it. The wall gets its strength from a sturdy base consisting of gravel — about 5 inches deep for short walls and about 7 inches for tall walls — which can help avoid sifting and allows water to drain under the wall. A 1-inch layer of coarse sand on top of the gravel will help with leveling. The first one or two tiers of stone are also buried to present a hardy, well-anchored base. Doing some basic calculations for the base and the wall makes it possible to determine the right amount of stone and gravel necessary for building a durable retaining wall. Gravel Needs Divide the base thickness of 5 to 7 inches — depending on the height of this wall — by 1,944 to determine the…