Quikrete Calculator
A Quikrete calculator divides volume by 0.60 cu ft per 80 lb bag: a 10 × 10 ft slab 4 in thick needs 55.56 bags, so 56, about $392 at $7 a bag.
Quikrete calculator: bags from volume
A Quikrete calculator converts the volume of your pour into 80 lb bags using the 0.60 cubic feet of mixed concrete that one bag yields. A 10 × 10 ft slab 4 inches thick is 33.33 cubic feet, which is 55.56 bags, so you buy 56.
Turn on the waste box to add 10%. For that slab it raises the order to 62 bags.
The formula in plain words
Cubic feet = length × width × (thickness in inches ÷ 12). Bags = cubic feet ÷ 0.60, rounded up to a whole bag. Cost = bags × the price you enter. With the waste box ticked, the bag count is multiplied by 1.1 before rounding up.
Worked example, a small patio slab
The slab is 10 ft × 10 ft and 4 inches thick. Bags are $7.
- Thickness: 4 ÷ 12 = 0.3333 ft
- Volume: 10 × 10 × 0.3333 = 33.33 ft³ (1.23 yd³)
- Bags: 33.33 ÷ 0.60 = 55.56, rounded up to 56
- Cost: 56 × $7 = $392
- With 10% extra: 61.11 bags, so 62 bags and $434
At 62 bags you are mixing about 4,960 pounds of dry material. That is a long day with a wheelbarrow or a mixer.
Worked example, a landing pad
A 4 ft × 6 ft pad at the back door, 4 inches thick.
- Volume: 4 × 6 × 0.3333 = 8 ft³
- Bags: 8 ÷ 0.60 = 13.33, rounded up to 14
- Cost: 14 × $7 = $98
- With 10% extra: 14.67, so 15 bags and $105
Bags by slab size
| Slab size | Thickness | Bags | With 10% extra |
|---|---|---|---|
| 3 × 4 ft | 4 in | 7 | 8 |
| 4 × 6 ft | 4 in | 14 | 15 |
| 8 × 10 ft | 4 in | 45 | 49 |
| 10 × 10 ft | 4 in | 56 | 62 |
| 10 × 10 ft | 6 in | 84 | 92 |
| 12 × 12 ft | 4 in | 80 | 88 |
How to measure
- Measure the finished surface, in feet. Use the forms’ inside dimensions.
- Use the actual concrete thickness, not the thickness of any gravel base under it.
- Add together separate pieces, such as a slab and a step.
- For small round holes, use the post hole concrete calculator instead of treating them as boxes.
Common mistakes
- Skipping the waste. Concrete does not give you a second try, and a half-filled form leaves a cold joint.
- Starting before everything is ready. Forms, base and tools should be done before the first bag is opened.
- Mixing batches at different times. Pour continuously so the surface stays even.
- Ignoring bag size. 60 lb and 80 lb bags yield different amounts.
- Pouring a slab without thinking about reinforcement or a base. A driveway or a heavy slab may need rebar and a compacted gravel layer, and local code may have rules for it.
When to switch to a truck
One cubic yard of concrete is 27 cubic feet, which is 45 bags at 0.60 cu ft each. The 10 × 10 ft slab is 1.23 cubic yards and 56 bags, or about 4,480 pounds of dry mix. Mixing that by hand or in a small drum mixer takes hours, and the early batches begin to set before you finish the last.
Get a ready-mix quote for the same volume. Many suppliers charge a short-load fee for small orders, so a slab this size may cost more per yard than a larger one. Price both ways, and count your time and rental costs for the mixer. For a pour over a yard, a truck or a mobile mixer often wins on effort. For a small pad, bags remain a sensible choice.
Related pages
The concrete bag calculator works in other bag sizes. For a larger pour, try the concrete slab calculator, and for small round holes use the post hole concrete calculator.
Frequently asked questions
Is this an official Quikrete tool?
No. It is an independent calculator that uses the yield printed on the bag, 0.60 cubic feet per 80 lb bag of standard mix. Always check the bag you buy, because different mixes and sizes have different yields.
How much does one 80 lb bag yield?
About 0.60 cubic feet of mixed concrete. A square foot of slab 4 inches thick is 0.333 cubic feet, so one bag covers about 1.8 square feet at that thickness.
What if I use 60 lb bags?
A 60 lb bag yields about 0.45 cubic feet. That means about one third more bags for the same job, so switch the unit or scale the count by 0.60 ÷ 0.45.
Does this work for fast-setting mixes?
Roughly, but check the label. Fast-setting and specialty mixes can have different yields, and some are meant for posts rather than slabs. Use the yield printed on your bag.
When is ready-mix better than bags?
As a rough guide, once a pour passes about a cubic yard, which is 45 bags, delivered ready-mix is worth pricing. It saves mixing time and gives a more consistent product. Slabs also have to be poured in one go, which is hard to do with bags.
How much water does a bag need?
The amount is printed on the bag. Too much water weakens the concrete, so measure it rather than guess. Follow the label for the amount and the mixing time.
Estimates only. Verify quantities with your supplier before purchasing.