Use the form below to calculate your yards and tons of material. The general rule of thumb is two to three inches deep for bark and soil. Many construction outfits go with six inches deep when it comes to gravel, especially if laying underneath a structure. You’ll want to consider compaction when ordering material and if tamping down the material you will need a bit more to complete the area. Playground bark is engineered for falls and the recommendation on installing playground chips is one inch of depth per one foot of distance of potential falls. Bark, soil and dirt are loaded by the yard whereas gravel and rock weighs out by the ton.