Concrete Slab Calculator
Cubic yards and bags for a slab, with the gravel base, rebar grid, and form boards on the same ticket.
Quick answer
A 10 x 10 ft slab 4 inches thick is 33.3 cubic feet, about 1.23 cubic yards, or 56 bags of 80 lb. Add 5 to 10 percent for uneven ground.
Measure the slab
5 to 10% covers uneven ground and spills
What goes with it
18 to 24 in on center is common
Adds a frost-depth reminder and goes into your copied order.
1.36 cubic yards of concrete, or 62 bags of 80 lb.
You need
1.36cubic yards
= 36.7 cu ft, including 10% extra · weighs about 5,500 lb poured
10 x 10 ft slab, 4 in thick
| Bag size | Bags | Total weight |
|---|---|---|
| 90 lb bag (0.675 cu ft) | 55 | 4,950 lb |
| 80 lb bag (0.60 cu ft) | 62 | 4,960 lb |
| 60 lb bag (0.45 cu ft) | 82 | 4,920 lb |
| 50 lb bag (0.375 cu ft) | 98 | 4,900 lb |
| 40 lb bag (0.30 cu ft) | 123 | 4,920 lb |
HaulOnce order ticket
Concrete order
Ticket no.
373856
Option A: Bags
Cheaper62 bags
Example price, enter yours
Option B: Ready-mix
1.5 cu yd
Rounded up to the nearest 0.25 yd.
Example, enter yours
Often included
Example, ask the plant
This order is under the short-load threshold, so the fee is included.
Ready-mix is cheaper above 1.4 cu yd. Bags saves $25.50 here.
Bags mean lifting 62 bags, 4,960 lb of dry mix, then mixing every one before the first sets. Past about a yard, most people order a truck.
Also on the list
Estimate from haulonce.com. Weights vary with moisture and supplier. Prices are examples unless you entered your own.
Haul Check
Typical 1,500 to 2,300 lb. We use the low end until you enter yours.
Check the Tire and Loading Information sticker on your driver's door jamb for your exact payload.
Bagged concrete hits your payload long before your bed is full.
That is 3,460 lb over your payload. You need 4 trips.
Split it into 4 loads of about 0.34 cu yd (1,240 lb) each, or get it delivered instead. At this many trips, delivery usually costs less than your time and fuel.
Using the low end of the typical payload range. Enter your own for an exact answer.
This checks hauling the bags yourself. Ready-mix arrives in the plant's truck.
What pros know
- An 80 lb bag yields about 0.6 cu ft, so a full cubic yard is 45 bags and 3,600 lb of dry mix to lift. Source
- Every bag size works out to the same 3,600 lb of dry mix per cubic yard. Smaller bags are easier to lift, not lighter in total. Source
- Set posts in a hole about 3 times the post's width, dug to about one third of the post's total length. Source
Ready to text or email your supplier:
“I'm picking up 62 bags of concrete mix (80 lb).”
Add your ZIP code above to include it.
What did you pay? (optional)
How thick should a slab be?
Common residential guidance, before local code:
- Walkway or sidewalk, 4 in
- Patio or shed pad, 4 in
- Driveway for cars, 5 in
- Heavy vehicles or RV pad, 6 in
Thicker slabs cost proportionally more: going from 4 to 5 inches adds 25 percent more concrete. Local codes and soil conditions set the real minimum, so check before you pour a driveway.
What goes under and in the slab
Most slabs sit on a compacted gravel base, commonly 4 inches or more, deeper where the ground freezes or drains poorly. The calculator adds the base as crushed stone with compaction built in; the crusher run calculator has more on that material.
Reinforcement is often a grid of rebar about 18 to 24 inches on center, or welded wire mesh, supported in the middle of the slab thickness. The calculator counts 20 ft bars for the grid, with 10 percent for overlaps. Form boards run around the perimeter.
Bags per slab
| Bag size | Yield per bag | Bags per cu yd | Bags for a 10 x 10 ft slab, 4 in |
|---|---|---|---|
| 90 lb bag | 0.675 cu ft | 40 | 50 |
| 80 lb bag | 0.6 cu ft | 45 | 56 |
| 60 lb bag | 0.45 cu ft | 60 | 75 |
| 50 lb bag | 0.375 cu ft | 72 | 89 |
| 40 lb bag | 0.3 cu ft | 90 | 112 |
Yields from the QUIKRETE Concrete Mix data sheet, before any extra for waste. Other brands are similar; check the bag.
Bags or a ready-mix truck
Bags make sense for post holes, small pads, and repairs. Past about a cubic yard, mixing becomes the problem: every bag has to be mixed and placed before the first one starts to set, which is hard for one or two people. Ready-mix arrives mixed, but plants often charge a short-load fee on small orders (commonly under about 4 yards; ask yours).
Enter your own bag price, ready-mix price, delivery fee, and short-load fee in the Order Ticket, and it shows the exact size where ready-mix becomes cheaper. The defaults are example prices, not local quotes.
Weight and hauling
Poured concrete weighs about 4,050 lb per cubic yard, roughly 150 lb per cubic foot. The dry mix in bags works out to 3,600 lb per yard in every bag size: 45 bags of 80 lb, or 90 bags of 40 lb, is the same weight.
A full-size half-ton pickup typically carries 1,500 to 2,300 lb, so one yard of bags is often two trips, and that is before you lift every bag twice. The Haul Check in the calculator works it out for your vehicle. Your exact payload is on the driver's door-jamb sticker.
Common mistakes
- Measuring thickness at the forms but not in the middle, where the subgrade dips.
- Pouring on loose soil without a compacted base.
- Rebar lying on the ground instead of supported mid-slab, where it does nothing.
- Skipping control joints. Concrete cracks; joints decide where.
Questions people ask
How much concrete do I need for a 10x10 slab?
At 4 inches thick, about 1.23 cubic yards, or 56 bags of 80 lb, before waste. At 6 inches, about 1.85 cubic yards.
How thick should a concrete patio be?
4 inches is standard for patios and walkways. Driveways for cars are often 4 to 5 inches, and 6 inches for heavy vehicles. Local code sets the minimum.
Do I need gravel under a concrete slab?
Usually, yes. A compacted base of 4 inches or more gives a stable, level, well-drained surface. Deeper bases help on clay and in freeze-thaw climates.
Do I need rebar in a concrete slab?
Many patios and driveways use rebar or wire mesh to hold cracks together. A grid about 18 to 24 inches on center is common. Follow local code for structural slabs.
How many bags of concrete for a slab?
Divide the slab's cubic feet by the bag yield (0.60 cu ft for an 80 lb bag). A 10 x 10 ft slab at 4 inches is 33.3 cubic feet, so 56 bags of 80 lb.
Sources
- QUIKRETE, Concrete Mix No. 1101 data sheet (bag yields, post setting method)
- QUIKRETE, Fast-Setting Concrete Mix spec data sheet (post setting yields)
- The Engineering ToolBox, Dirt and Mud: Densities (dry, moist, and wet soils, sand, and gravel)
- NHTSA, Tires: the Tire and Loading Information placard on the driver's door jamb
Last reviewed: . How we calculate
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