How To Calculate Concrete For A Slab
A step-by-step guide to accurately determine the amount of concrete needed for your slab project. Use the interactive calculator below for instant cubic yard and bag estimates.
Step-by-Step Calculation Guide
Calculating concrete for a slab involves a simple three-step process:
- Measure Your Slab: Accurately measure the length and width in feet, and the desired depth in inches. Standard slab depth is 4 inches for patios and walkways.
- Apply the Formula: Use the formula:
(Length × Width × Depth) / 12 = Cubic Feet. Then convert to cubic yards by dividing by 27. - Add Waste Factor: Add 5-10% to your total volume to account for spillage, uneven ground, and over-excavation.
The calculator above automates this process, providing both bulk (cubic yards) and bagged concrete estimates.
Related Tools & Guides
Explore our other construction calculators and guides to plan your project thoroughly:
- Concrete Calculator - For footings, columns, and walls.
- Circular Slab Calculator - For round patios and pads.
- How To Level Ground For A Slab - Site preparation guide.
- Gravel Calculator - Calculate base material for your slab.
Privacy Note
This concrete slab calculator runs entirely in your browser. No data you enter is sent to our servers or stored anywhere. All calculations happen locally on your device for your privacy and security.
Frequently Asked Questions
What is the formula to calculate concrete for a slab?
The basic formula is: (Length in feet × Width in feet × Depth in inches) / 12 = Volume in cubic feet. Then, divide the cubic feet by 27 to get cubic yards. For example, a 12ft × 10ft slab at 4 inches deep is (12 × 10 × 4) / 12 = 40 cubic feet, or 40 / 27 ≈ 1.48 cubic yards.
How do I account for waste when ordering concrete?
It's recommended to add 5-10% extra concrete to your calculated volume to account for spillage, over-excavation, and uneven subgrade. For a slab requiring 2 cubic yards, order 2.1 to 2.2 cubic yards. For bagged concrete, round up to the nearest whole bag.
Can I use this calculator for a circular slab?
This calculator is designed for rectangular or square slabs. For a circular slab, the formula is: (3.1416 × (Radius in feet)² × Depth in inches) / 12. You can use our dedicated Circular Slab Calculator for that purpose.