Project Calculators
Project calculators pre-set every decision for a specific job — shape, material, depth, waste, and compaction are all baked in. You just enter the dimensions of your project.
All project calculators
- Fence post concrete calculator — N holes × (diameter, depth) minus post volume. For 4×4 and 6×6 fence posts on residential fences.
- Sonotube calculator — N tubes × (diameter, depth). For deck footings, pergola posts, sign posts.
- Gravel driveway calculator — length × width × depth for a residential driveway. 4–6 inch depth with 25% compaction.
- Concrete slab cost calculator — slab cost with national price ranges. 4-inch patio or 6-inch driveway.
- Asphalt driveway cost calculator — asphalt cost with national price ranges. 2-inch resurface or 4-inch full-depth.
When to use a project calculator vs the generic one
- Project calculator: you know the job. Fence posts on a 6 ft privacy fence, gravel driveway, etc. The defaults are right; you just enter dimensions.
- Generic calculator: you're not sure what the right defaults are, or you have a custom job that doesn't fit a project template. You pick every option yourself.
For a 12×12 patio, either works. For a non-standard job (a triangular courtyard, a circular fire pit area), the generic calculator is more flexible.
How project defaults are chosen
Each project preset bakes in a "right answer" for the most common version of that job. For a fence post, the calculator assumes:
- 4×4 post (square)
- 12 inch hole diameter
- 24 inch hole depth
- 10% waste
- No compaction (concrete doesn't compact in the ground)
You can override any of these. The defaults just remove the decisions you don't want to make.
Common project mistakes
- Wrong depth for fence posts: should be 1/3 of the post length in the ground. For a 6 ft post, that's 2 ft; for an 8 ft post, 2.5–3 ft.
- Skipping the gravel base for fence posts: 4–6 inches of gravel under the post so water drains away from the buried end.
- Too thin a gravel layer for a driveway: 4 inches minimum; 6 inches for heavy vehicles or clay subgrade.
- Underestimating the slab size for concrete: measure twice, order 10% extra.