How many bags of concrete do I need? Enter your slab, footing, or post hole dimensions and get an instant count for 40lb, 60lb, or 80lb bags with cost estimates.
Tip: 80lb bags are more efficient and cost-effective for larger pours like slabs and footings.
Recommended: 10% for spillage and uneven subgrade
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Last updated March 31, 2026 by our expert review team
Easier to carry
Yield: 0.3 cu ft
At 4": 0.9 sq ft
Price: $4.5
Most common
Yield: 0.45 cu ft
At 4": 1.4 sq ft
Price: $5.5
Best value
Yield: 0.6 cu ft
At 4": 1.8 sq ft
Price: $6.5
Ehsan Ghazanfari
Licensed Structural Engineer
FISE-certified structural engineer with 11+ years designing bridges, retaining walls, and foundations. MSc from Aalto University.
See full profileCherry Jane Limbago
Licensed Civil Engineer & Master Plumber
Licensed civil engineer and master plumber with 10+ years in structural design, estimation, and project management. Currently Project Engineer at Universal Robina Corporation.
See full profileUpdated March 2026
How we verify our calculators| Project Size | 2" Deep | 4" Deep | 6" Deep |
|---|---|---|---|
| 2' × 2' | 2 | 3 | 5 |
| 4' × 4' | 5 | 9 | 14 |
| 6' × 6' | 10 | 20 | 30 |
| 8' × 8' | 18 | 36 | 54 |
| 10' × 10' | 28 | 56 | 84 |
Based on national averages for Quikrete and Sakrete bags at major retailers. Prices vary 10-20% by region.
Mix one bag at a time in a wheelbarrow. Rushing multiple bags leads to weak spots and cold joints that crack within the first winter.
Add water slowly (about 3 quarts per 80lb bag) until you hit a thick oatmeal consistency. Too much water is the #1 cause of weak DIY concrete. Follow Quikrete's mixing instructions for best results.
Score control joints every 8 to 10 feet with a groover tool while still wet. Without them, random cracks appear within 6 months.
Cover fresh concrete with plastic sheeting and keep it damp for 7 days minimum. Skipping this cuts final strength by up to 50%.
Never pour when temps will drop below 50°F within 48 hours. Water in the mix can freeze before curing, leaving crumbly concrete.
Dampen the subgrade before pouring. Dry ground pulls moisture out too fast, weakening the bottom layer. For post holes, try Quikrete Fast-Setting for same-day results.
Building steps? Use our concrete steps calculator for stair-specific volume and cost estimates.
Need to dig out an area first? Our excavation calculator estimates dirt removal before you pour.
For slabs and large pours, use our concrete slab calculator to estimate cubic yards and ready-mix costs.
For sonotubes and round footings, our concrete cylinder calculator handles the circular volume math for you.
The real challenge with concrete isn't the math; it's the ground underneath. Our calculator starts with the standard volume formula (length × width × depth), but the overage factor is where experience matters. Flat, well-compacted ground with forms in place might only need 5% extra. But if you're pouring over rocky, uneven soil or on a slight slope, bump that to 15-20% because concrete always finds the low spots and fills in more than you planned.
Formula
Volume (cu ft) = Length × Width × (Depth ÷ 12)
Bags Needed = Volume ÷ Bag Yield × (1 + Waste %)
How many bags of concrete do I need?
Multiply length x width x (depth / 12) for cubic feet, then divide by bag yield: 0.60 cu ft for 80lb, 0.45 for 60lb, 0.30 for 40lb. Use the Quikrete coverage calculator to double-check.
How much is a yard of concrete?
Ready-mix runs $125 to $175/yd delivered, with short-load fees under 3 to 4 yards. Mixing from 80lb bags costs $160 to $195/yd in materials but avoids minimums.
How many bags in a cubic yard?
45 bags of 80lb, 60 bags of 60lb, or 90 bags of 40lb. Above 1 yard, most pros switch to ready-mix.
How much does a yard of concrete weigh?
About 3,900 lbs wet (roughly 2 tons), dropping to 3,600 lbs after 28-day cure. A single yard exceeds most half-ton truck ratings.
How much is concrete per yard?
$125 to $150/yd rural, $150 to $200/yd near cities, plus $50 to $100 delivery. Under 1 cubic yard, bagged is usually cheaper.
What does an 80lb bag cover?
0.60 cu ft of mixed concrete. At 4" thick, that covers about 1.8 sq ft. A typical fence post hole takes 1 to 2 bags.
How thick should concrete be?
4" for patios and walkways, 6" for driveways, 8 to 12" for footings. See the concrete slab thickness guide for details.
Bags vs ready-mix: when to switch?
The break-even is about 1 cubic yard (45 bags of 80lb). Below that, bags win. Above 1 yard, ready-mix saves hours of labor.
Planning concrete steps?
Stairs require a cumulative volume calculation different from flat slabs. Use our concrete steps calculator for accurate step estimates.
Adding too much water
If you can pour it like a milkshake, add dry mix. Proper concrete holds its shape when cut with a trowel.
Skipping the subgrade prep
Remove all organic material, compact the soil, and add 2 to 4 inches of compacted gravel for slabs 4" or thicker.
Pouring in the wrong weather
Below 50°F slows curing dangerously; above 90°F causes flash-set cracking. Aim for 50 to 80°F with overcast skies.
Not using forms or edge support
Without forms, edges spread thin. Stake 2×4 forms every 2 to 3 feet and brace corners firmly.
Mixing too many bags at once
Concrete sets in 30 to 45 minutes. Mix 2 to 3 bags at a time and keep a steady pace.
Forgetting control joints
Cut joints every 8 to 10 feet so cracks follow planned lines instead of wandering randomly.
Standard backyard patio. Use 80lb bags if hand-mixing, or order 1.5 yards of ready-mix to account for waste.
Set posts in dry Quikrete and add water. The fast-set method lets you hang fence boards the same day.
Right at the bags-vs-truck threshold. If your supplier has a short-load fee under $100, ready-mix saves 3 hours of mixing.
Important Disclaimer
These estimates are for planning purposes only. Actual costs vary by location, material availability, and project complexity. Always get at least 3 local quotes. This calculator does not replace professional advice.