Concrete Patio Calculator

1. Choose the shape: rectangle, circle or L-shape.
2. Enter the dimensions in feet, and the thickness in inches (4 inches is typical for a patio).
3. Set the number of patios and a 5 to 10 percent waste allowance.
4. Read the result: cubic yards to order, plus cubic feet, bags, weight and the area.

Here is what each result line means:

A concrete patio calculator estimates the concrete for a patio of any common shape, not just a rectangle. Patios are often round or L-shaped, and getting the area right for the shape is the key to ordering the right amount.

It works for a rectangular patio, a round patio measured across the diameter, and an L-shape made of two rectangles. The tool finds the area for the shape, multiplies by the thickness, and adds a waste allowance. For a footing, column or mixed shape beyond these, use the general concrete mix calculator for the mix, or the cement calculator for the binder, and the water cement ratio calculator for mix water.

The only thing that changes with the shape is how the area is found. Once there is an area, the volume is the same for every shape: area times thickness, divided by 27 for cubic yards.

1. For a rectangle, multiply length by width. For a circle, take pi times the radius squared, with the radius half the diameter.
2. For an L-shape, add the areas of the two rectangles.
3. Multiply the area by the thickness in feet, and by the number of patios, for the volume in cubic feet.
4. Add the waste allowance, then divide by 27 for cubic yards and by the bag yield for a bag count.

Suppose you are pouring a rectangular patio 16 feet by 12 feet at 4 inches, with 10 percent waste.

Calculation: the area is 16 x 12 = 192 sq ft. Volume = 192 x 0.333 = 64 cu ft, or 2.37 cu yd. Adding 10 percent waste gives 70.4 cu ft, which is 2.61 cu yd, about 118 eighty-pound bags and roughly 5.3 short tons.

The lesson: at over 2.5 cubic yards, this patio is past the point where mixing 118 bags by hand makes sense. A short-load ready-mix delivery is the easier call.

Shape and Measuring

A round patio holds less than the square it fits inside, and an L-shape must be split into rectangles. Measuring the shape correctly is the main source of error, not the arithmetic.

Thickness

Thickness multiplies the whole area. Most patios are 4 inches; going thicker for a heavier use adds concrete across the entire surface.

Sub-base and Over-excavation

A soft or uneven base soaks up concrete below grade, the main reason a real pour beats the geometry and the reason for a waste allowance.

Edges and Curves

Curved or stepped edges, a thickened perimeter or an integral border all change the volume. Break an irregular patio into rectangles and circles and add them.

The shape decides how you measure, and how much concrete the same footprint uses. A round patio uses less than the rectangle it sits in, while an L-shape is simply two rectangles added.

For an odd shape that is none of these, split it into parts you can measure, work out each, and add the volumes.

Ordering Concrete for a Patio

Size the order in cubic yards and add waste before you call the supplier, so you neither run short nor over-order.

Costing a Bag Job

For a small patio, the bag count tells you how many bags to buy and whether hand mixing is realistic.

Comparing Shapes

Try a round patio against the rectangle it would replace to see how much concrete, and cost, the shape saves.

1. Treating a Round Patio as a Square

A circle uses about four-fifths of the square around it. Measuring the diameter but ordering for a square over-orders by a fifth.

2. Not Splitting an L-shape

An L-shape is two rectangles. Measuring one overall length and width counts the missing corner and over-orders.

3. Mixing Up Feet and Inches

Entering thickness in feet instead of inches shrinks the result twelvefold. Keep the plan sizes in feet and thickness in inches.

4. Forgetting a Waste Allowance

An uneven base and spillage mean the exact geometry runs short. Keep 5 to 10 percent.

5. Ignoring a Thickened Edge or Border

A patio with a deepened edge or a border holds more than a flat slab. Add those parts separately.

The arithmetic is exact; the usefulness depends on measuring the shape correctly and on the thickness and waste you enter.

It depends on the size and thickness. A 16 by 12 foot patio at 4 inches needs about 2.61 cubic yards with waste, roughly 118 eighty-pound bags. Enter your shape and dimensions above for the exact figure.

Measure the diameter across, halve it for the radius, and the area is pi times the radius squared. A 12 foot round patio is about 113 square feet, so at 4 inches it needs about 1.5 cubic yards with waste. The tool does this when you pick the circle shape.

Split it into two rectangles, work out each area, and add them. The L-shape option takes both rectangles and totals the concrete, so you do not count the missing corner.

Usually 4 inches for foot traffic and furniture. Go thicker only if the patio will carry heavier loads. The required thickness comes from your plans or local practice; this tool estimates volume.

A small patio can be bagged: a 10 by 10 foot patio at 4 inches is about 62 eighty-pound bags with waste. A larger one runs well over 100 bags, which is usually the point to switch to ready-mix. The tool gives the count for your patio.

About 150 pounds per cubic foot. A 16 by 12 foot, 4 inch patio weighs around 5 short tons of concrete, so the sub-base must be firm and level to carry it without settling.

Yes, a 5 to 10 percent waste allowance for an uneven sub-base and spillage. Running short mid-pour risks a cold joint, so the small margin is worth it.

No. The calculation runs entirely in your browser and nothing you enter is stored or sent anywhere.

• QUIKRETE Concrete Mix 1101 data sheet (QUIKRETE; bag yields 0.60, 0.45 and 0.30 cu ft).
• National Ready Mixed Concrete Association (NRMCA; ready-mixed concrete and ordering).
• American Cement Association (American Cement Association; what concrete and cement are).