Concrete Slab Calculator
0% (Exact)
5% (Recommended)
10% (Safe)
Estimation Results
Total Volume Required:
0 Cubic Yards
Volume in Cubic Feet:
0 ft³
80lb Bags (Pre-mix):
0 bags
60lb Bags (Pre-mix):
0 bags
Est. Material Cost (Bulk):
$0.00
How to Calculate Concrete for Your Project
Planning a concrete project requires precise measurements to ensure you order enough material without excessive waste. Whether you are pouring a patio, a driveway, or a foundation footing, understanding the volume of concrete needed is the first step to a successful installation.
This Concrete Slab Calculator helps you determine exactly how many cubic yards or pre-mix bags you need based on the dimensions of your pour.
The Concrete Volume Formula
To calculate the volume of a concrete slab manually, you need to find the cubic footage and then convert it to cubic yards, which is the standard unit for ordering ready-mix concrete.
The formula is: Length (ft) × Width (ft) × Thickness (ft) = Cubic Feet
Note: Since thickness is usually measured in inches, you must divide the inch value by 12 to convert it to feet before multiplying.
To get Cubic Yards: Cubic Feet ÷ 27 = Cubic Yards
Pre-Mix Bags vs. Ready-Mix Truck
Should you buy bags or order a truck? It depends on the volume:
- Under 1 Cubic Yard: It is usually more economical and convenient to use pre-mix bags (60lb or 80lb) found at home improvement stores.
- 1 to 2 Cubic Yards: This is the "gray area" where renting a tow-behind mixer or ordering a small load might be feasible, though bags are still an option if you have help.
- Over 2 Cubic Yards: Ordering a ready-mix truck is typically the best option. Mixing this amount by hand is labor-intensive and makes it difficult to achieve a consistent pour.
Pro Tip: Always add a 5-10% safety margin (waste factor) to your calculation. Spillage, uneven subgrades, and form measuring errors can lead to a shortage, which is disastrous during a concrete pour.
Standard Slab Thicknesses
Choosing the right thickness is vital for the longevity of your slab:
- 4 Inches: Standard for walkways, patios, and residential floor slabs.
- 5-6 Inches: Recommended for driveways and garage floors that support passenger vehicles.
- 6+ Inches: Heavy-duty driveways for RVs or heavy equipment.