Concrete patio planning: bags or delivery?

1. Measure volume, not just surface area

For a 10 × 10 ft footprint at an entered 4-inch thickness: 100 × (4 ÷ 12) = 33.3333 cubic ft, or 1.234568 cubic yards before allowance. With 10% extra, volume becomes 36.6667 cubic ft, or 1.358025 cubic yards.

Use inside form dimensions after site preparation, not just the intended footprint. NRMCA describes additional concrete for dimensional and placement contingencies; an allowance cannot replace accurate measurements or an approved design. Thickened edges, footings and steps require separate volumes.

2. Use the mix's listed wet-volume yield

At a listed yield of 0.60 cubic ft per bag, 36.6667 ÷ 0.60 = 61.1111, rounded up to 62 bags. At 0.45 cubic ft, the same adjusted volume needs 82 bags. Keep the volume unrounded until the final package calculation.

Bag weight is a purchasing label, not a universal yield conversion. Different mixes can produce different volumes. Read the specific product data sheet. A quoted 80-lb bag at $7 would give a hypothetical $434 mix-only purchase; it excludes mixer rental, delivery, labor and preparation.

3. Compare complete quotes, not just per-yard prices

Suppose a supplier hypothetically quotes $160 per cubic yard with a 0.25-yard increment and $150 delivery/short-load fees. Rounding the required 1.358025 yards to that assumed increment gives 1.50 yards: $240 concrete plus $150 fees, or $390 before tax and other costs. Actual supplier minimums and increments can be different.

The planner displays an upward-rounded 1.359 yd³ calculation at three decimals, not an approved order quantity. Ask the supplier how to turn that estimate into an order. Capture the bag scenario, switch to ready-mix and enter the quote. Enter the supplier's order increment and minimum load in the planner; it will round the buy quantity accordingly. Use Other for separately quoted fees and document their scope.

Do not treat a lower entered subtotal as proof of a better pour. Mixing capacity, placement time, access, weather, staffing and suitable equipment matter. The worksheet cannot assess those site conditions.

4. Separate the base from the slab

A 100 sq ft footprint with an entered 4-inch base depth has a geometric in-place volume of 1.234568 yd³. That is not automatically the loose delivered volume or tonnage. Density, moisture, grading and compaction differ by material. Obtain the supplier's conversion and installation requirements before ordering.

The optional base row exists so this work is not forgotten, but it does not prescribe a sufficient base or infer soil conditions. Forms, reinforcement, vapor barriers, joints, drainage and finishing consumables remain separately specified items.

5. Bring these questions to the supplier

• What mix specifications are required by the approved project?
• What are the minimum load, order increment and complete delivered charges?
• Can the vehicle reach the pour, and is pumping or additional handling needed?
• What placement time is included, and how is an adjustment or unused mix handled?
• For bags, what is the exact listed yield and required mixing equipment?

Use the patio worksheet to record the answers, unpriced items and quote date. Confirm structural or load-bearing work with the appropriate professional and local authority; the calculator is a material-quantity aid.