Estimate bags of concrete needed for slabs, footings, post holes, and pads.
Bagged concrete is a pre-mixed blend of cement, sand, gravel, and other additives sold in individual bags at hardware stores and building supply centers. Instead of ordering ready-mix concrete from a truck (which requires a minimum order), bagged concrete offers flexibility for smaller projects—you can buy exactly what you need and mix it on-site. It's ideal for post holes, stepping stones, small patios, repairs, and any project under one cubic yard.
Bagged concrete comes in several sizes: 80 lb bags are the standard and most economical choice for larger pours, 60 lb bags balance cost and handleability for one-person jobs, and 50 lb or 40 lb bags suit smaller projects and repairs. Each bag size has a different yield (how much volume it produces when mixed), so selecting the right size affects both your cost and labor. A 10×10 ft patio at 4 inches thick, for example, requires roughly 56 bags of 80 lb concrete—a significant quantity that arrives at your doorstep without heavy machinery.
This calculator removes the math from your estimate. Enter your length, width, and thickness, choose your bag size, and instantly see how many bags you need. It automatically accounts for waste and rounding up (you can't order partial bags), so you'll know your exact shopping list before heading to the store.
Volume = length × width × (thickness ÷ 12). Divide by bag yield and round up. Always buy 5–10% extra for waste.
| Bag size | Approx yield |
|---|---|
| 80 lb | 0.60 cu ft |
| 60 lb | 0.45 cu ft |
| 50 lb | 0.375 cu ft |
About 45 bags of 80 lb concrete equal one cubic yard.
Yes — add 5–10% for waste, spills, and form irregularities.
80 lb bags are standard for slabs. 60 lb bags are easier to handle for one person.
Results are estimates for planning purposes. Verify with product labels and local requirements before purchasing materials.
Estimating concrete bags starts with calculating the total volume of your project in cubic feet. Multiply the length by the width to get the area, then multiply by the thickness in feet — divide inches by 12 to convert. Divide the resulting cubic footage by the yield of your chosen bag size and round up to the nearest whole bag.
The formula is: Bags needed = (Length ft × Width ft × Thickness in ÷ 12) ÷ Bag yield
Always buy at least 5–10% extra. Running short mid-pour forces you to stop, which creates cold joints — weak seams where fresh concrete meets partially set concrete.
| Bag size | Approx. yield | Bags per cu yd | Best for |
|---|---|---|---|
| 80 lb | 0.60 cu ft | ~45 bags | Slabs, footings, large pads |
| 60 lb | 0.45 cu ft | ~60 bags | General use, easier to lift |
| 50 lb | 0.375 cu ft | ~72 bags | Small repairs, post holes |
| 40 lb | 0.30 cu ft | ~90 bags | Small patches, anchoring |
| Project type | Dimensions | Thickness | 80 lb bags needed |
|---|---|---|---|
| Small shed pad | 8×10 ft | 4 in | 45 |
| Standard patio | 10×12 ft | 4 in | 67 |
| Driveway apron | 12×16 ft | 4 in | 107 |
| Sidewalk section | 4×20 ft | 4 in | 45 |
| Fence post hole | 10 in dia | 36 in deep | 1–2 per post |
| Deck footing | 12 in dia | 36 in deep | 2–3 per footing |
Here is a worked example for a 12×16 ft shed pad at 4 inches thick:
Step 1: Convert thickness to feet: 4 ÷ 12 = 0.333 ft
Step 2: Calculate volume: 12 × 16 × 0.333 = 63.9 cubic feet
Step 3: Divide by bag yield: 63.9 ÷ 0.60 = 106.5 bags
Step 4: Round up and add 10% waste: 107 × 1.10 = 118 bags
Purchase 118 bags of 80 lb concrete for this project. If you switch to 60 lb bags, you would need approximately 156 bags.
A 10×10 ft slab at 4 inches thick requires about 33.3 cubic feet of concrete. Using 80 lb bags that yield 0.60 cubic feet each, you need about 56 bags. Add 10% for waste, so purchase 62 bags.
One cubic yard equals 27 cubic feet. At 0.60 cubic feet per 80 lb bag, you need approximately 45 bags to fill one cubic yard of space.
A standard 10-inch diameter post hole at 36 inches deep needs roughly 1 to 2 bags of 80 lb concrete per post. Use the quick-set variety for post holes — it sets in about 20-40 minutes without mixing.
Multiply length × width × thickness (in feet) to get cubic feet. Divide by 0.60 for 80 lb bags, 0.45 for 60 lb bags. Round up and add 10% for waste.
Use bagged concrete for projects under 1 cubic yard (about 45 bags of 80 lb). For larger projects like full driveways or foundations, ready-mix concrete is more economical and far less labor-intensive.
Standard bagged concrete reaches initial set in 24-48 hours. You can walk on it after 24 hours and drive on it after 7 days. Full strength (4000 PSI) is reached after 28 days of curing.
An 80 lb bag of standard concrete mix costs approximately $6-$8 at most hardware stores. Specialty mixes like fast-setting or high-strength run $8-$12 per bag.
Yes. Dampen the subgrade before pouring to prevent dry soil from pulling moisture out of the fresh concrete, which weakens the final product. Do not make it muddy — just moist.
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