Concrete Volume & Mix Calculator
Calculate how many cubic yards of concrete you need for a slab, footing, or pad, including a waste allowance. Use this before ordering ready-mix concrete to avoid costly shortfalls or excess.
About this calculator
Concrete volume is calculated by multiplying the three dimensions of the pour area and converting to cubic yards, which is the standard ordering unit. The base volume is: V = L × W × (T/12), where L is length in feet, W is width in feet, and T is thickness in inches (divided by 12 to convert to feet). This calculator then applies a 10% waste factor (multiplying by 1.1) to account for spillage, over-excavation, and uneven subgrade — a standard industry practice. If a custom mix ratio is specified, an additional 5% is added to cover the extra material needed for batching. The final result gives you the total volume to order in cubic yards. Always round up to the nearest quarter yard when placing a ready-mix order.
How to use
Suppose you are pouring a driveway slab that is 20 ft long, 10 ft wide, and 4 inches thick, with a standard mix ratio. Step 1: Base volume = 20 × 10 × (4/12) = 20 × 10 × 0.333 = 66.67 ft³. Step 2: Apply 10% waste factor: 66.67 × 1.1 = 73.33 ft³. Step 3: Convert to cubic yards: 73.33 / 27 ≈ 2.72 yd³. Step 4: No custom mix ratio, so no extra 5% applies. Order 3 cubic yards to be safe. This covers the slab with sufficient margin for minor over-pours.
Frequently asked questions
Why do I need to add a waste factor when ordering concrete?
A waste factor accounts for the inevitable losses that occur during a concrete pour. Subgrade surfaces are rarely perfectly flat, so concrete fills low spots and irregular areas beyond the nominal thickness. Spillage during chute delivery, overflow at form edges, and residual concrete left in the truck drum all contribute to material loss. The standard 10% waste allowance is widely recommended by ready-mix suppliers and contractors to ensure you have enough concrete to complete the pour without running short mid-job, which can cause cold joints and structural weaknesses.
How do I convert concrete volume from cubic feet to cubic yards?
Ready-mix concrete in the United States is sold by the cubic yard, so converting your calculated volume is essential before placing an order. Since 1 cubic yard equals 27 cubic feet (3 ft × 3 ft × 3 ft), simply divide your cubic foot volume by 27 to get cubic yards. For example, 81 cubic feet divided by 27 equals exactly 3 cubic yards. Most suppliers require a minimum order and charge in quarter-yard increments, so always round your result up to the nearest quarter yard to ensure you receive enough material.
What mix ratio should I choose for a residential concrete slab?
The mix ratio describes the proportion of cement, sand, and aggregate in the concrete batch, and the right choice depends on the structural demands of the application. A standard 1:2:3 ratio (one part cement, two parts sand, three parts aggregate) produces general-purpose concrete suitable for most residential slabs, sidewalks, and driveways, typically achieving around 3,000 psi compressive strength. For higher-strength applications like structural footings or driveways subject to heavy vehicle loads, a richer mix or a specified 4,000 psi ready-mix is preferable. Most homeowners ordering ready-mix simply specify the desired psi strength and let the batch plant determine the mix proportions automatically.