*Bag calculations assume standard concrete density of ~133 lbs/ft³ dry mix yielding ~145 lbs/ft³ cured.
How to Calculate Concrete for Slabs
Whether you are pouring a simple patio, a walkway, or a heavy-duty driveway, accurately calculating the volume of concrete required is the first step to a successful project. Ordering too little results in expensive "short load" fees or cold joints, while ordering too much is money poured down the drain.
The Concrete Volume Formula
Concrete is sold by volume, specifically in Cubic Yards. To determine how much you need, you must calculate the volume of your slab in cubic feet and convert it.
Note: Don't forget to convert your thickness from inches to feet by dividing by 12 before multiplying!
Recommended Thickness Guide
4 Inches: The standard for residential sidewalks, patios, and garage floors (light vehicles).
5 Inches: Recommended for driveways with moderate traffic or heavier SUVs.
6 Inches: Heavy-duty driveways, RV pads, or agricultural floors.
Why Add a Wastage Margin?
No sub-base is perfectly flat. If your ground is slightly uneven, you will use more concrete than the mathematical perfect volume. Spillage during the pour and concrete sticking to tools also accounts for loss. We recommend adding 5% to 10% extra to your order (often called the "margin of safety") to ensure you don't run out before the job is finished.