How Much Concrete for a 8×8 slab, 4" Thick?
This calculator is pre-filled to estimate the concrete for a 8×8 slab (4" thick). Change any field to match your project, and enter your local price for a precise cost.
Quick answer: An 8×8 slab at 4 inches thick needs about 0.83 cubic yards of concrete (22 cu ft) — roughly 38 80 lb bags.
Concrete Slab calculator
How it's calculated: Length ft × width ft × (thickness in ÷ 12) = cubic feet; add 5% waste and divide by 27 for cubic yards. An 80 lb bag yields about 0.6 cu ft.
How to estimate concrete slab
- A 4-inch slab suits patios and walkways; go to 5-6 inches for driveways and anything carrying vehicle weight.
- Ready-mix is sold by the cubic yard; for slabs over ~1 cu yd it is almost always cheaper than bagged concrete.
- Order about 5-10% extra to cover uneven subgrade and spillage. You cannot add a second batch to wet concrete.
- Keep the slab damp for the first week - misting or covering it slows the cure and produces a harder, less dusty surface.
- Have helpers, screed board and floats ready before the truck arrives; ready-mix waits for no one and drivers bill standby time.
Frequently asked questions
How Much Concrete for a 8×8 slab, 4" Thick?
An 8×8 slab at 4 inches thick needs about 0.83 cubic yards of concrete (22 cu ft) — roughly 38 80 lb bags.
How many 80 lb bags are in a cubic yard?
An 80 lb bag yields about 0.6 cubic feet, so roughly 45 bags make up one cubic yard. Bagged mix only makes sense for small jobs.
How thick should a concrete slab be?
4 inches is standard for patios and shed floors, 5-6 inches for driveways and garages where vehicles park.
How long before I can walk or drive on a new slab?
Keep foot traffic off for 24-48 hours and vehicles off for at least a week. Concrete reaches most of its design strength at 28 days, and keeping it damp the first week makes it noticeably stronger.
Do I need rebar or wire mesh in a slab?
Patios and walkways over a compacted base usually get wire mesh or fiber-reinforced mix to hold cracks tight; driveways and garage floors commonly add rebar. Reinforcement controls cracking rather than preventing it, which is why control joints are cut every 8-12 feet on a 4-inch slab.
What goes under a concrete slab?
A 4-inch layer of compacted gravel over firm, undisturbed soil. The base drains water and gives even support - pouring over soft or freshly filled ground is the most common reason slabs crack and settle.
Should I pour it myself or hire a contractor?
A small pad you can mix from bags is a reasonable DIY job. Once you are ordering a truck you have a short window to screed and finish the whole pour, so line up experienced help - most homeowners hire out anything much past a one-yard slab.