One cubic yard of concrete takes about 45 bags of 80 lb mix, 60 bags of 60 lb mix, or 90 bags of 40 lb mix. A 10×10 ft slab 4 inches thick, with 10% extra, is 1.36 cubic yards — about 62 bags of 80 lb or 82 bags of 60 lb. Run your own size in the free QtyLab concrete calculator.
Pouring a 10×12? See how many bags of concrete for a 10×12 slab — 74 bags of 80 lb at 4 in, with 5 in and 6 in counts.
Bags per cubic yard
| Bag size | Typical yield | Bags per cubic yard | Bags per cubic foot |
|---|---|---|---|
| 80 lb | 0.60 ft³ | 45 | 1.7 |
| 60 lb | 0.45 ft³ | 60 | 2.2 |
| 40 lb | 0.30 ft³ | 90 | 3.3 |
Yields are typical Quikrete-style planning figures. Check the label on the bag you are buying — the yield is printed on it.
Slab chart: bags for common sizes
4 inches thick, 10% extra included, bags rounded up. Click a size to open it in the calculator.
| Slab | Cubic yards | 80 lb bags | 60 lb bags |
|---|---|---|---|
| 4 × 4 ft (landing, AC pad) | 0.22 | 10 | 14 |
| 10 × 10 ft (patio, shed) | 1.36 | 62 | 82 |
| 10 × 12 ft | 1.63 | 74 | 98 |
| 12 × 12 ft | 1.96 | 88 | 118 |
| 10 × 20 ft | 2.72 | 123 | 163 |
Past about 1 to 1.5 cubic yards, compare the price of bags against a ready-mix delivery — see “Bags vs ready-mix” below.
Buying bagged concrete is straightforward until you try to figure out how many bags to load into the truck. Too few and you are mixing a second batch mid-pour; too many and you are stuck with heavy bags you may not use.
This guide shows how to turn slab or footing measurements into cubic feet, then into typical 60 lb and 80 lb bag counts. When you want a faster check, use QtyLab’s free concrete calculator.
Start with volume, not bag count
Concrete quantity is volume. Measure the space you will fill, convert to cubic feet (or cubic yards), then divide by the yield printed on the bag. Guessing from square footage alone skips thickness and usually leaves you short.
For a rectangular slab or pad:
Length (ft) × width (ft) × thickness (ft) = cubic feet
Thickness is often given in inches. Convert inches to feet by dividing by 12. A 4-inch slab is 4 ÷ 12 = 0.333 feet.
To get cubic yards, divide cubic feet by 27:
Cubic feet ÷ 27 = cubic yards
One cubic yard equals 27 cubic feet. Ready-mix trucks usually quote yards; bagged mix is easier to think about in cubic feet and bag yields.
Typical bag yields: 60 lb and 80 lb
Bag labels list how much volume one bag makes when mixed as directed. Yields vary by brand and mix type, but these Quikrete-style figures are common planning estimates:
- 60 lb bag ≈ 0.45 cubic feet
- 80 lb bag ≈ 0.60 cubic feet
Always read the bag you buy. High-strength, crack-resistant, or fast-setting mixes can list different yields. Use the label number when it differs from the estimates above.
Quick conversion formulas
Once you know cubic feet:
- 60 lb bags ≈ cubic feet ÷ 0.45 (round up)
- 80 lb bags ≈ cubic feet ÷ 0.60 (round up)
Per cubic yard (27 cu ft), that works out to roughly 60 bags of 60 lb mix or about 45 bags of 80 lb mix, before any waste factor. Labels vary, so treat those as planning numbers only.
Worked example: a small patio slab
Suppose you are pouring a small patio: 10 feet long × 8 feet wide × 4 inches thick.
- Convert thickness: 4 ÷ 12 = 0.333 ft
- Volume: 10 × 8 × 0.333 ≈ 26.64 cubic feet
- In yards: 26.64 ÷ 27 ≈ 0.99 cubic yards (about 1 yard)
Bag counts before waste:
- 60 lb: 26.64 ÷ 0.45 ≈ 59.2 → round up to 60 bags
- 80 lb: 26.64 ÷ 0.60 ≈ 44.4 → round up to 45 bags
Add a waste buffer for uneven subgrade, forms that bow, and mixing spills. A 5–10% allowance is typical for DIY slabs. At 10%:
- Volume with waste: 26.64 × 1.10 ≈ 29.3 cu ft
- 60 lb: 29.3 ÷ 0.45 ≈ 66 bags
- 80 lb: 29.3 ÷ 0.60 ≈ 49 bags
That is a lot of mixing by hand. For roughly a cubic yard or more, many DIYers compare bag cost and labor to a small ready-mix delivery. Use the concrete calculator to plug in your dimensions and waste percent and see both bag sizes at once.
Footings, steps, and other shapes
Footings are often long, narrow trenches. Use the same formula: length × width × depth in feet. If depth is 12 inches and width is 16 inches, that is 1.0 ft × 1.33 ft × length.
For steps or stepped pads, calculate each rectangular section separately and add the volumes. For a round column or post footing, use π × radius² × height (all in feet), then convert to bags the same way.
Irregular pads work best when you split them into rectangles. Measure each piece, total the cubic feet, then divide by bag yield.
Bags vs ready-mix: when to switch
Bagged concrete works well for post holes, small pads, repairs, and sites a truck cannot reach. Ready-mix (or mix-on-site trucks) often makes more sense near a full yard or more, when you want a continuous pour, or when labor matters more than per-bag price.
Either way, get the volume right first. Wrong math costs more than the difference between 60 lb and 80 lb bags.
How much extra should you buy?
Plan on about 5–10% extra for slabs with fair forms and a level base. Consider a bit more if the subgrade is rough or you are new to mixing. Confirm return policies for unopened bags before you leave the store.
Do not skip the waste factor and hope leftover dry mix will cover a short pour. Once you start finishing, you need enough wet concrete on hand.
Common mistakes when estimating bags
- Leaving thickness in inches: Multiply length × width × (inches ÷ 12), not length × width × inches.
- Ignoring waste: Forms, spills, and low spots eat volume.
- Trusting a generic yield without checking the label: Your bag may not be 0.45 or 0.60 cu ft.
- Mixing bag sizes in one estimate: Pick 60 lb or 80 lb so the count matches what you load.
- Forgetting footings or thickened edges: Edge beams add cubic feet fast.
Use the free QtyLab concrete calculator
Skip the spreadsheet. Open the free QtyLab concrete calculator, enter length, width, and depth, set a waste percentage, and read cubic yards, cubic feet, and estimated 60 lb and 80 lb bag counts. It is built for the same planning math in this guide.
Planning other outdoor materials? Try the gravel calculator for base and drainage, the fence calculator for posts and panels, and the mulch calculator for beds. If you are covering garden beds, see how much mulch do I need for depth and bag tips. Browse more free tools on the QtyLab home page.
Once you know your bag count, shop for the mix type that matches your project—general purpose, high strength, or fast setting—and follow the bag’s water and curing instructions. Compare bag yield and bag weight at your local store or online retailer; heavier 80 lb bags mean fewer trips but harder lifts.
Planning note: These estimates are for planning and purchasing guidance only. Actual yield depends on the product label, mix design, water content, and placement conditions. Confirm bag yield and project specs before buying, and consider ready-mix for larger pours. Follow local code and manufacturer instructions for structural work.
Shopping list for a 10×10 slab (4 in)
- 62 bags of 80 lb concrete mix (or 82 × 60 lb) — shop 80 lb concrete mix
- About 40 linear ft of 2×4 form boards plus stakes — lumber yard or home center
- 1 mixing tub or wheelbarrow and a mortar hoe — shop mixing tubs
- 1 bull float or magnesium float, plus an edger — shop finishing tools
- Reinforcement, if your plan calls for it (wire mesh or rebar) — shop wire mesh
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Setting fence posts? See how much fencing you need — it includes concrete per post. Pouring on a gravel base? Use the gravel calculator. Laying pavers instead of pouring? The paver calculator counts pavers, base gravel and sand — see how many pavers do I need.
FAQ
How many bags of concrete are in a yard?
About 45 bags of 80 lb mix, 60 bags of 60 lb mix, or 90 bags of 40 lb mix, based on typical yields of 0.60, 0.45, and 0.30 cubic feet per bag. A cubic yard is 27 cubic feet.
How many 80 lb bags of concrete for a 10×10 slab?
At 4 inches thick with 10% extra, a 10×10 slab is 1.36 cubic yards, or about 62 bags of 80 lb mix (82 bags of 60 lb).
Should I buy 60 lb or 80 lb bags?
They cost about the same per cubic foot. 80 lb bags mean fewer bags to open and mix; 60 lb bags are easier to lift and carry. Buy whichever you can handle all day.
When should I order ready-mix instead of bags?
Once a job goes past roughly 1 to 1.5 cubic yards, hand-mixing 60+ bags gets slow and tiring, and ready-mix may cost about the same. Many plants charge a short-load fee for small orders, so get a quote before deciding.
How much extra concrete should I buy?
About 10% covers uneven ground, spills, and form bulges. Use more if the base is rough or the depth varies.