Hardscaping

Patios and walls: paver count from the patio area and the paver face size (plus waste), paver-patio cost, retaining-wall block count from the wall face area, retaining-wall cost, polymeric-sand bags for the joints, and the gravel base and bedding sand under the pavers. Coverage is a labeled typical — confirm on the product. ⚠️ Walls over about 3–4 ft usually need an engineer and a permit.

Planning estimate: this is a planning estimate. Coverage varies by product (bag size, compaction, waste, slope and how tightly you pack). Buy about 5–10% extra and confirm the coverage printed on the product before you order.
Engineer & permit for tall walls: Retaining walls taller than about 3–4 ft (or holding a surcharge/slope) usually need an engineer's design and a permit. Confirm height limits and drainage with your local building department.

Every Hardscaping tool is calculated server-side — visible immediately — with its formula, a worked example and a reference table, and works on the quantities you measure and the prices you enter. Background reading is in the guides.