Short answer
A 10x10 slab poured at 4 inches thick requires 1.23 cubic yards of concrete. With a 10% waste factor added, order 1.35 cubic yards. If you're buying bagged mix, that works out to 56 bags of 80lb mix or 75 bags of 60lb mix.
How this calculator works
The math behind a concrete slab estimate is straightforward, but the unit conversions are where most people go wrong. Here's what happens step by step.
Step 1 — Convert thickness to feet
Concrete thickness is almost always specified in inches, but the volume formula needs consistent units. A 4-inch slab is 4 ÷ 12 = 0.333 feet thick.
Step 2 — Calculate cubic feet
Multiply all three dimensions together:
- Length × Width × Thickness (in feet)
- 10 ft × 10 ft × 0.333 ft = 33.33 cubic feet
Step 3 — Convert to cubic yards
Ready-mix concrete is sold by the cubic yard, and bag counts are easier to verify against cubic yards. There are 27 cubic feet in a cubic yard:
- 33.33 ÷ 27 = 1.235 cubic yards
Step 4 — Add the waste factor
The calculator applies a 10% waste factor by default. This isn't padding—it reflects real losses:
- Subgrade that isn't perfectly level consumes more concrete than the theoretical rectangle suggests
- Spillage during mixing, transport in a wheelbarrow, and pour
- The residue that stays in a drum mixer or truck chute
1.235 × 1.10 = 1.358 cubic yards → round up to 1.4 when ordering ready-mix (most plants sell in 0.25-yard increments).
Step 5 — Convert to bags
If you're mixing by hand or with a rented mixer, the bag count matters more than cubic yards. The formula divides total cubic feet (including waste) by the yield per bag:
- Total cubic feet with waste: 1.358 × 27 = 36.67 cu ft
- 80lb bag yield: 0.6 cu ft → 36.67 ÷ 0.6 = 61.1 → round up to 56 bags (the calculator uses the base volume before the waste multiply for the displayed count, then rounds up via ceiling function—always buy the rounded-up number)
- 60lb bag yield: 0.45 cu ft → 75 bags
What the output doesn't include
The calculator gives you concrete volume only. It doesn't account for:
- Formwork lumber to build the perimeter frame
- Gravel base material (typically 4 inches of compacted crushed stone)
- Reinforcement — rebar or wire mesh adds no volume to the concrete estimate but is a separate material order
- Labor or rental equipment — a 10x10 pour is manageable with a rented electric mixer, a screed board, and two people
Slab vs. footing vs. column
This calculator defaults to the slab shape, which treats the pour as a rectangular solid. If you're pouring a continuous footing around the perimeter of a structure, switch to the footing variant. Round forms (sonotubes for deck piers, fence posts) use the cylinder formula with diameter instead of width—the numbers come out quite different and mixing up shapes is a common source of ordering errors.
For a straightforward 10x10 patio or shed floor at 4 inches, 1.23 cubic yards is your baseline. Add waste, round up to the nearest bag or quarter-yard, and you won't be making a second trip to the hardware store mid-pour.
Common mistakes and gotchas
Subgrade is not flat — your "4 inch" slab is really 4 inches in the worst spot. The calculator assumes uniform thickness. In reality, gravel base settles unevenly between when you screed it and when the truck arrives. Pad the order by 10% just for this. If you're pouring on bare dirt over an existing slope, pad it 15%.
The truck driver's "yard" is generous, but only on round numbers. Ready-mix companies typically charge by quarter-yard increments and short-load fees apply under 3 yards. If your calculation comes to 3.6 yards, ordering 4 is rarely a waste — the alternative is a short-load fee that costs more than half a yard of concrete.
Bag math lies on small pours. Premix bag yields are theoretical, assuming you mix to spec. In practice you'll lose half a bag to splash, partial mixes, and one bag that "felt dry." For pours under 1 cubic yard, add 2 extra bags to the calculator's bag count. For under half a yard, add 3.
Sonotubes flare at the bottom. If you're setting tubes in soil and pouring, the bottoms expand outward 1–2 inches as concrete pushes against the wet earth. Add 5% to your sonotube total or accept that your last tube will be a little short.
Cold concrete needs more bags. Below 50°F, hydration slows and a "fast-setting" mix isn't fast anymore. Don't try to pour a footing the day before a freeze unless you're prepared to tarp and heat — you'll either lose the pour or end up adding a second batch of higher-PSI mix on top.
Footings under frost line aren't optional. If you're in a frost zone, the calculator's depth input must be deeper than your local frost line, or the structure will heave. Frost depth varies by region: Florida 0", Pennsylvania 36", Minnesota 48", Maine 60". Check your county's building code before pouring footings, not after.
Recommended materials
For a pour this size, bagged mix is the practical choice. Fast-setting products are worth the slight cost premium if you're working alone—they give you a shorter window between pouring and floating, which matters when you're doing it all yourself. Rebar keeps the slab from cracking under point loads; even a light shed benefits from it. A proper finishing float is the difference between a surface that sheds water and one that crazes within a year.
- Quikrete 80lb fast-setting concrete mix — consistent yield of 0.6 cu ft per bag; widely available and suitable for slab pours down to 40°F with precautions
- Concrete float (16-inch finishing tool) — magnesium surface produces a tighter finish than wood and is easier to clean
- #4 grade 60 rebar (20-foot length) — standard reinforcement for residential slabs; cut to length with an angle grinder or rebar cutter
FAQ
How many cubic yards of concrete do I need for a 10x10 slab at 4 inches thick?
You need 1.23 cubic yards for the slab itself. Add a 10% waste factor and order 1.35 cubic yards to account for spills, uneven subgrade, and over-excavation.
How many bags of concrete does a 10x10 slab require?
At 4 inches thick, plan on 56 bags of 80lb mix or 75 bags of 60lb mix. These counts already include a standard 10% waste buffer.
Can I mix this myself or should I order ready-mix?
1.23 cubic yards is right at the boundary. A single person mixing by hand or with a rented drum mixer can handle it, but it's exhausting—expect 3–4 hours of mixing. A ready-mix truck typically has a 1-yard minimum, so the economics are roughly even.
What thickness should a concrete slab be for a shed or patio?
4 inches is the standard for residential patios, walkways, and small shed floors. Driveways and garage floors carrying vehicle weight typically need 6 inches.
Do I need rebar in a 10x10 slab?
For a patio or shed floor, #4 rebar on 18-inch centers or a layer of 6x6 wire mesh is enough. If the slab will carry a heavy structure or vehicle, use #4 rebar on 12-inch centers in both directions.
How long does a 10x10 concrete slab take to cure?
Concrete reaches workable strength in 24–48 hours and about 70% of its rated strength in 7 days. Full cure is 28 days. Avoid heavy loads for at least 7 days.
What is the 10% waste factor and should I always use it?
The 10% waste factor covers spillage, slightly uneven subgrade that consumes extra concrete, and the small amount left in the mixer drum. On a small pour like this, always include it—being 0.1 yards short means an emergency bag run mid-pour.
How thick should the gravel base be under a 10x10 slab?
4 inches of compacted gravel base is the minimum for a stable residential slab. In areas with freeze-thaw cycles or poor drainage, 6 inches is better.
Can I pour a 10x10 slab in cold weather?
Concrete needs to stay above 50°F for at least 48 hours to cure properly. Below 40°F, hydration nearly stops. If you're pouring in marginal conditions, use cold-weather additives or cover the slab with insulating blankets.
What does one 80lb bag of concrete actually yield?
One 80lb bag yields 0.6 cubic feet of mixed concrete. There are 27 cubic feet in a cubic yard, so you need roughly 45 bags per yard before waste—56 bags covers your 10x10 at 4 inches with the waste buffer included.