How to Estimating Concrete & Cement Bags
Calculating the right amount of concrete is crucial for any construction project, whether you're pouring a patio slab, a driveway, or footings for a deck. Ordering too little results in expensive delays and weak "cold joints," while ordering too much is a waste of money.
The Basic Formula
The general formula for calculating concrete volume for a slab
is:
Length × Width × Thickness = Volume
Since concrete is sold by the Cubic Yard (in the US) or Cubic Meter, you typically need to convert your measurements.
- 1 Cubic Yard = 27 Cubic Feet
- Premix Bags: A standard 80lb bag yields approximately 0.6 cubic feet.
- Waste Factor: Always add 5-10% extra for spillage and uneven sub-grades. Our calculator adds a standard 5% buffer automatically.
Common Projects
4" Slab (Patio/Sidewalk)
Standard thickness for residential walking surfaces.
6" Slab (Driveway)
Recommended for driveways holding heavy vehicles.