Outdoor & Structural
Concrete Calculator & Project Planner
Work out how much concrete a patio or slab actually needs, including waste, base gravel, and whether ready-mix or bags makes more sense. You get quantities, an estimated budget, and a shopping list you can take to the store.
Before you build
Slab thickness, reinforcement, base depth, and footing requirements vary by use, soil, climate, and local building code. Verify structural and code requirements before you build.
Common questions
How thick should a concrete patio be?
Four inches is the common thickness for patios, walkways, and shed pads. Driveways and anything carrying vehicle weight are usually five to six inches, often with rebar. Local code and soil conditions can change that, so check before you pour.
How much concrete waste should I plan for?
Ten percent is a reasonable default for a small slab. Uneven subgrade is the biggest driver — if your excavation is rough or the ground is soft, plan closer to fifteen percent. Running short mid-pour is far more expensive than a little extra.
Is it cheaper to use bags or ready-mix?
Bags usually win below about one cubic yard, where delivery minimums and short-load fees dominate. Past that, ready-mix is normally both cheaper and dramatically less work — one cubic yard is roughly sixty 60 lb bags mixed by hand.
Do I need gravel under a concrete slab?
A compacted base spreads load and gives water somewhere to go, which is what keeps a slab from cracking as the ground moves. Four inches of compactable gravel is a common planning figure for patios. Local frost depth and drainage conditions matter here.
What usually comes next
Projects that tend to follow a concrete job.
ProjectKit provides planning estimates only. Actual requirements, costs, installation methods, structural requirements, permits, safety requirements, and building codes vary. Verify critical specifications before purchasing materials or beginning work. Read the full terms.