Concrete Slab Calculator: Yards, Bags and Cost
Concrete slab calculator
- Concrete to order
- – cu yd (– cu ft)
- 80 lb bags
- – bags
- 60 lb bags
- – bags
- Ready-mix
- –
How we calculate this
- Volume in cubic feet = length × width × (thickness in inches ÷ 12).
- We add your waste percentage, then divide by 27 to get cubic yards.
- Bags = total cubic feet ÷ yield per bag, rounded up. Yields come from the manufacturer: 80 lb = 0.6 cu ft , 60 lb = 0.45 cu ft (Quikrete Concrete Mix No. 1101 data sheet (revised October 2022)).
- Cost = bags × the price per bag shown above. Taxes and delivery are not included.
A 10 × 10 ft slab that is 4 inches thick holds 33.3 cubic feet of concrete. That’s 56 bags of 80 lb mix with no extra, or 62 bags if you add 10% for spills and an uneven base. Change the numbers above to size your own slab.
At the Home Depot prices we checked in , bagged concrete works out to $281–$291 per cubic yard for the concrete alone.
Quick answers for common sizes
| Slab | Cubic yards | 80 lb bags | 60 lb bags |
|---|---|---|---|
| 4 × 4 ft, 4 in | 0.22 | 10 $62.40–$64.70 | 14 $65.52–$67.90 |
| 6 × 6 ft, 4 in | 0.49 | 22 $137.28–$142.34 | 30 $140.40–$145.50 |
| 8 × 8 ft, 4 in | 0.87 | 40 $249.60–$258.80 | 53 $248.04–$257.05 |
| 10 × 10 ft, 4 in | 1.36 | 62 $386.88–$401.14 | 82 $383.76–$397.70 |
| 10 × 12 ft, 4 in | 1.63 | 74 $461.76–$478.78 | 98 $458.64–$475.30 |
| 12 × 12 ft, 4 in | 1.96 | 88 $549.12–$569.36 | 118 $552.24–$572.30 |
| 10 × 20 ft, 4 in | 2.72 | 123 $767.52–$795.81 | 163 $762.84–$790.55 |
| 12 × 12 ft, 6 in | 2.93 | 132 $823.68–$854.04 | 176 $823.68–$853.60 |
| 10 × 20 ft, 6 in | 4.07 | 184 $1,148.16–$1,190.48 | 245 $1,146.60–$1,188.25 |
Two things stand out in the table:
- Bag size barely changes the cost. A cubic foot of concrete costs $10.40–$10.78 in 80 lb bags and $10.40–$10.78 in 60 lb bags at the prices we checked in . The small differences in the table come from rounding up to whole bags. Pick the size you can lift and mix comfortably: with 60 lb bags you carry less per trip but mix a third more bags.
- Thickness matters as much as area. Going from 4 to 6 inches adds 50% more concrete, so a 12 × 12 ft slab jumps from 88 to 132 bags of 80 lb mix (with 10% extra).
What it costs
| Product | Price range | Where and when we checked |
|---|---|---|
| Quikrete Concrete Mix, 80 lb bag | $6.24–$6.47 per 80 lb bag No price shown near CA 95814 | Home Depot ·
|
| Quikrete Concrete Mix, 60 lb bag | $4.68–$4.85 per 60 lb bag No price shown near CA 95814 | Home Depot ·
|
These are shelf prices for Quikrete Concrete Mix at Home Depot stores near our reference ZIP codes. Open the details in the table to see each store and date. If a store near one of our reference ZIP codes didn’t show a price, the table says so under the range.
The bag price only covers the concrete. Quikrete’s instructions also call for forms staked in place and a tamped, compacted base. This calculator doesn’t price those yet.
Bags or ready-mix? The calculator also shows how many cubic yards you’d order from a ready-mix truck. We don’t list ready-mix prices because they come from local suppliers, not store shelves. Ask a few suppliers near you for their price per cubic yard and any delivery fees, type it into the calculator, and compare it with the bag total.
How to measure
- Length and width: measure in feet. For inches, divide by 12: 10 ft 6 in is 10.5 ft.
- Thickness: enter inches, not feet. Measure the depth of your forms in a few spots. If the base is uneven, use the average and keep some extra for waste.
- Odd shapes: split an L-shaped slab into two rectangles, run the calculator for each and add the results.
- Thin pours: Quikrete designs this mix for pours 2 inches thick or more.
Common mistakes
- Entering thickness in feet. A 4-inch slab is a third of a foot deep. Typing 4 as feet gives you 12 times too much concrete. The calculator asks for inches to avoid this.
- Using the wrong yield. Some online guides use 2/3 of a cubic foot for an 80 lb bag. Quikrete’s data sheet says about 0.60. On a 10 × 10 ft slab at 4 inches, that’s 50 bags versus 56. Check the yield printed on your bag.
- Skipping the extra. Spills, form bulges and low spots in the base all use up concrete. Quikrete says to fill the form to full depth, working continuously from one end to the other, and to avoid partial-depth fills, which can lead to cold joints. Running out halfway makes that hard, so buy some extra.
- Mixing too many bags at once. Quikrete says to allow at least 1 cubic foot of mixer capacity for each 80 lb bag you mix at one time, with about 6 pints of water per 80 lb bag to start and no more than about 9 (4 to 7 pints for a 60 lb bag).
- Forgetting control joints and curing. Quikrete recommends cutting 1-inch-deep control joints every 6 to 8 feet, keeping the slab curing for 5 days in warm weather (70°F or higher) or 7 days between 50°F and 70°F, and protecting it from freezing for the first 48 hours.
A slab for a driveway, a shed or anything structural may need a specific thickness, reinforcement or a permit. Check your local building code before you pour.
Frequently asked questions
- How many 80 lb bags of concrete make a cubic yard?
- About 45. Quikrete rates an 80 lb bag of its Concrete Mix at about 0.60 cubic feet, and a cubic yard is 27 cubic feet, so 27 ÷ 0.60 = 45 bags before any extra for waste.
- How many 60 lb bags of concrete make a cubic yard?
- About 60. A 60 lb bag yields about 0.45 cubic feet according to Quikrete, and 27 ÷ 0.45 = 60 bags before waste.
- How many bags of concrete do I need for a 10x10 slab 4 inches thick?
- The slab holds 33.3 cubic feet of concrete. That is 56 bags of 80 lb mix or 75 bags of 60 lb mix with no extra, or 62 and 82 bags if you add 10% for waste.
- How much water does a bag of concrete need?
- Quikrete says to start with about 6 pints of water for an 80 lb bag of Concrete Mix and expect no more than about 9 pints. For a 60 lb bag, start with about 4 pints and expect no more than about 7.