Order too little and you get a cold joint halfway through the pour. Order too much and you pay for concrete you dump. Here is how to get the number right, using a real example.
Step 1: Measure the area, not the plan
Measure length and width in feet. For a patio that is not a rectangle, split it into rectangles and add them. Then check the depth of the dug-out area in several spots. Uneven ground is the biggest reason people run short.
Step 2: Choose the thickness
A standard patio slab is 4 inches thick. If a heavy grill, hot tub or occasional vehicle will sit on it, ask a local pro about 5 to 6 inches.
Step 3: Do the math
Cubic feet = length (ft) x width (ft) x thickness (in) / 12. Divide by 27 for cubic yards.
Example: a 12 x 14 ft patio, 4 in thick. 12 x 14 x 4 / 12 = 56 cubic feet = 2.07 cubic yards. Add 10% for waste and uneven ground: 61.6 cubic feet = 2.28 yards.
Step 4: Bags or ready-mix?
| Bagged (80 lb) | Ready-mix truck | |
|---|---|---|
| Amount | about 103 bags | about 2.3 yards |
| Example cost* | 103 x $6.50 = about $670 | 2.3 x $150 = about $345 plus delivery |
| Reality | Over 8,000 lb of mix to carry and mix by hand | Poured fast, but a short-load fee may apply |
*Example prices only. Check your local prices. Many suppliers charge a fee for small loads, so call and ask before deciding. For a job this size, most people compare both and often choose ready-mix.
Mistakes that cause problems
- No slope: a patio needs a slight fall away from the house, commonly about 1/8 to 1/4 inch per foot, so water does not pool.
- No joints: concrete cracks as it shrinks. Control joints cut roughly every 8 to 10 feet in a 4 in slab help cracks form in straight lines.
- Soft base: compact 4 inches of gravel under the slab. A soft base leads to settling.
- Adding water to make it easier: extra water weakens the finished concrete.
Ordering tip
Have forms, base and helpers ready before the truck arrives. The concrete starts setting as soon as it is mixed, and you do not want to be still leveling the ground when it arrives.
Enter your own measurements in the slab calculator to get yards and bags instantly. After the pour, read how long concrete takes to dry and cure.
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General information and estimates only. Follow your local building code and your supplier's instructions.