Key numbers
- Formula: L (ft) × W (ft) × T (in) ÷ 324 = cubic yards
- 12 × 16 ft at 4 in: 2.37 yd³, order 2¾ yd³ or 118 × 80 lb bags
- 1 yd³ covers 81 ft² of patio at 4 in, 65 ft² at 5 in
- Fall: ⅛ in per foot drops a 16 ft patio 2 in
On this page
- How to use the Concrete Patio Calculator
- How to calculate concrete for a patio
- Concrete for common patio sizes
- How thick should a concrete patio be?
- Round, curved and L-shaped patios
- Patio slope, base and joints
- Bags or ready-mix for a patio?
- Common mistakes when estimating patio concrete
- Frequently asked questions
How to use the Concrete Patio Calculator
- 1Choose the shapePick slab / pad or round slab. Each shape uses its own volume formula.
- 2Pick your unitsEvery dimension has its own unit menu (in, ft, yd, cm or m); changing one converts that number so the size stays the same. The US / Metric switch sets all fields to feet and inches or meters and centimeters and resets them to typical values.
- 3Enter the dimensionsType the length (default feet), width (default feet) or thickness (default inches). Measure the inside of the forms and the depth in several places.
- 4Set waste and quantityUse the waste slider (0 to 20%, default 10%) and allow more on uneven ground. If you have several identical pours, enter how many.
- 5Read the resultsSee the volume in cubic yards, cubic feet and cubic meters, the ready-mix order rounded up to ¼ yard, the number of 90, 80, 60, 50 and 40 lb bags rounded up, and the weight at the density you choose (150, 145 or 140 lb/ft³).
- 6Price it and save itPick a pricing basis (per cubic yard, per cubic meter or per bag of the highlighted size) and enter your local price for a material cost. Use Add to project to total several pours, and Copy link to share the exact result.
Results update as you type. Back to the calculator ↑
How to calculate concrete for a patio
A patio is a slab, so the volume is length × width × thickness. Patios are measured in feet and thickness in inches, and ready-mix is sold by the cubic yard, so one formula covers all three:
Cubic yards = length (ft) × width (ft) × thickness (in) ÷ 324
The 324 is 12 inches per foot × 27 cubic feet per cubic yard. For cubic feet, divide by 12 instead.
- Mark out the patio and measure inside the form boards. Round fractions of an inch up.
- Pick the thickness. About 4 in is common for a patio that only carries foot traffic and furniture; heavier loads need more (see the thickness table below).
- Run the formula or enter the size above. The calculator also gives cubic feet, cubic metres, bag counts and weight.
- Add 10% for spillage and an uneven base, then round up to the next ¼ yd³ or whole bag.
Worked example: 12 × 16 ft patio, 4 in thick
- 12 × 16 × 4 ÷ 324 = 2.37 yd³ (64 ft³)
- Add 10%: 2.61 yd³ → order 2¾ yd³ of ready-mix
- In bags: 70.4 ft³ ÷ 0.60 ft³ = 118 × 80 lb bags (157 × 60 lb)
- Weight in place at 150 lb/ft³: about 9,600 lb
Concrete for common patio sizes
These are the patio sizes people search for most, at 4, 5 and 6 in thick. “Order” includes 10% extra rounded up to ¼ yd³; bag counts are 80 lb and 60 lb bags at 4 in, with the 10% included.
| Patio | Area (ft²) | 4 in (yd³) | Order at 4 in | 80 lb bags | 60 lb bags | 5 in (yd³) | Order at 5 in | 6 in (yd³) | Order at 6 in |
|---|---|---|---|---|---|---|---|---|---|
| 10 × 10 ft | 100 | 1.23 | 1½ | 62 | 82 | 1.54 | 1¾ | 1.85 | 2¼ |
| 10 × 12 ft | 120 | 1.48 | 1¾ | 74 | 98 | 1.85 | 2¼ | 2.22 | 2½ |
| 12 × 12 ft | 144 | 1.78 | 2 | 88 | 118 | 2.22 | 2½ | 2.67 | 3 |
| 12 × 16 ft | 192 | 2.37 | 2¾ | 118 | 157 | 2.96 | 3½ | 3.56 | 4 |
| 12 × 20 ft | 240 | 2.96 | 3½ | 147 | 196 | 3.70 | 4¼ | 4.44 | 5 |
| 14 × 14 ft | 196 | 2.42 | 2¾ | 120 | 160 | 3.02 | 3½ | 3.63 | 4 |
| 16 × 16 ft | 256 | 3.16 | 3½ | 157 | 209 | 3.95 | 4½ | 4.74 | 5¼ |
| 16 × 20 ft | 320 | 3.95 | 4½ | 196 | 261 | 4.94 | 5½ | 5.93 | 6¾ |
| 20 × 20 ft | 400 | 4.94 | 5½ | 245 | 326 | 6.17 | 7 | 7.41 | 8¼ |
| 20 × 30 ft | 600 | 7.41 | 8¼ | 367 | 489 | 9.26 | 10¼ | 11.11 | 12¼ |
Past about 1 yd³ (45 × 80 lb bags) most people order ready-mix: 118 bags for a 12 × 16 ft patio is over 9,000 lb of dry mix to lift and mix by hand. To price the job, take the order quantity to the concrete patio cost page.
How thick should a concrete patio be?
Most patios are poured about 4 in thick. Go to 5–6 in where the slab will carry a hot tub, an outdoor kitchen or a vehicle. These are common practice, not code; follow your plans, local code and any equipment maker’s pad specification.
| Thickness | cm | ft² covered by 1 yd³ | yd³ per 100 ft² | 80 lb bags per 100 ft² (+10%) | Weight per ft² |
|---|---|---|---|---|---|
| 3.5 in | 8.9 | 92.6 | 1.08 | 54 | 44 lb |
| 4 in | 10.2 | 81 | 1.23 | 62 | 50 lb |
| 5 in | 12.7 | 64.8 | 1.54 | 77 | 62.5 lb |
| 6 in | 15.2 | 54 | 1.85 | 92 | 75 lb |
Each extra inch on a 12 × 16 ft patio adds 0.59 yd³, about 30 more 80 lb bags. The concrete slab thickness calculator works the other way: enter the concrete you have and it tells you how thick the patio will come out.
Round, curved and L-shaped patios
Choose Round slab in the calculator for circles. Volume is π × radius² × thickness. At 4 in thick:
| Diameter | Area (ft²) | Cubic yards | Order (+10%) | 80 lb bags (+10%) |
|---|---|---|---|---|
| 8 ft | 50.3 | 0.62 | ¾ yd³ | 31 |
| 10 ft | 78.5 | 0.97 | 1¼ yd³ | 48 |
| 12 ft | 113.1 | 1.40 | 1¾ yd³ | 70 |
| 14 ft | 153.9 | 1.90 | 2¼ yd³ | 95 |
| 16 ft | 201.1 | 2.48 | 2¾ yd³ | 123 |
For an L-shaped patio, split it into rectangles and use Add to project to total them. A 16 × 12 ft patio with an 8 × 8 ft grill extension at 4 in is 2.37 + 0.79 = 3.16 yd³, ordered as 3½ yd³. A half-circle is half the round figure for its diameter. For a freeform curve, measure the longest length and the average width and treat it as a rectangle, then keep the 10% allowance.
Patio slope, base and joints
These three details change how the patio performs more than its size does, and the base changes the order.
- Slope. Water must run away from the house. Many builders use about ⅛–¼ in per foot: a 16 ft patio drops 2–4 in. If the base is graded to the same fall the thickness stays even and the volume does not change.
- Base. A compacted gravel base is common under patios. 4 in of gravel under a 12 × 16 ft patio is 2.37 yd³, roughly 3.3 tons; the gravel calculator sizes it for your stone. A base ½ in low across the same patio adds 0.30 yd³ of concrete.
- Control joints. QUIKRETE’s data sheet calls for joints cut 1 in deep every 6–8 ft, so a 12 × 16 ft patio usually gets one joint across the width and one or two along the length.
- Finish. Broom, exposed aggregate and stamped finishes do not change the volume. Compare them in types of concrete finishes.
Bags or ready-mix for a patio?
Bags make sense for small patios and pads under about ½ yd³ (around 23 × 80 lb bags). Between ½ and 1 yd³, compare a small-load delivery with buying bags and renting a mixer. Above 1 yd³, which is any patio larger than about 8 × 10 ft at 4 in, ready-mix is usually less work and avoids cold joints between batches.
Ask the plant before you book
Give the plant the order quantity (2¾ yd³ for the 12 × 16 ft example), the use (“4 in exterior patio”) and how close the truck can get. Ask about its minimum load and any short-load fee; both vary by supplier.
Common mistakes when estimating patio concrete
- Using inches as feet. 12 × 16 × 4 is 768, not cubic feet. Divide by 324 for yards: 2.37 yd³.
- Forgetting the step or landing. A step down from the back door is a separate pour; use the concrete steps calculator and add it to the project.
- Skipping the extension. Grill pads and walkway tails are often left out of the first sketch.
- Ordering the exact volume. Without the 10% allowance a small spill or form bulge leaves you short.
- Mixing up bag sizes. 45 × 80 lb bags make a yard, but it takes 60 × 60 lb bags.
For any other flat slab, such as a shed base or garage floor, use the concrete slab calculator.
FAQ
Frequently asked questions
How much concrete do I need for a 12×16 patio?
A 12 × 16 ft patio 4 in thick needs 2.37 cubic yards (64 ft³). With 10% extra, order 2¾ yd³ of ready-mix, or buy 118 bags of 80 lb concrete. At 5 in thick it needs 2.96 yd³ (order 3½).
How many bags of concrete do I need for a 10×10 patio?
62 bags of 80 lb concrete, or 82 bags of 60 lb, for a 10 × 10 ft patio 4 in thick with 10% extra. The exact volume is 1.23 yd³ (33.3 ft³), so a 1½ yd³ ready-mix order is less lifting.
How many yards of concrete for a 20×20 patio?
4.94 cubic yards at 4 in thick, so order 5½ yd³ with 10% extra. At 5 in a 20 × 20 ft patio needs 6.17 yd³ (order 7) and at 6 in 7.41 yd³ (order 8¼).
How much concrete for a 14×14 patio?
A 14 × 14 ft patio (196 ft²) 4 in thick needs 2.42 yd³: order 2¾ yd³, or buy 120 bags of 80 lb concrete including 10% extra. At 5 in it needs 3.02 yd³ (order 3½).
How thick should a concrete patio slab be?
Most patios are poured about 4 in thick, and 5–6 in where a hot tub, heavy grill island or vehicle may sit. That is common practice, not code: check local code and any equipment maker's pad spec. Each extra inch on a 12 × 16 ft patio adds 0.59 yd³.
How much concrete for a round patio?
Use π × radius² × thickness. A 12 ft round patio 4 in thick needs 1.40 yd³ (order 1¾ yd³ or 70 × 80 lb bags with extra). A 16 ft circle needs 2.48 yd³ (order 2¾).
How much concrete for an L-shaped patio?
Split it into two rectangles and add them. A 16 × 12 ft patio with an 8 × 8 ft extension, 4 in thick, is 2.37 + 0.79 = 3.16 yd³. Order 3½ yd³ with 10% extra.
How much slope does a concrete patio need?
Many builders use about ⅛–¼ in per foot away from the house, so a 12 ft patio drops 1.5–3 in. Slope does not change the volume if the base is graded to the same fall; check your plans or local code for the figure.
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Last reviewed October 11, 2026 by M Bilal. Found an error? Tell us.