Concrete Depot
Concrete Calculators & Tools
Dashboard-ready report tool

Concrete Bag Calculator for Slab

Estimate how many concrete bags you need for a slab. Enter slab size, thickness, bag yield, waste, and cost to build a printable Concrete Depot report.

Measurement inputs

Live calculation updates as you type.

Slab bag estimate
Used in the saved report.
Switches starter units.
Use 1 for a single slab. Enter at least 1 slab.
Example: 20 ft. Enter a length greater than 0.
Example: 12 ft. Enter a width greater than 0.
Example: 4 in. Enter a thickness greater than 0.
10% is common for normal jobs. Waste cannot be negative.
Check your bag label for exact yield. Choose a valid bag yield.
Concrete volume made by one bag. Enter a bag yield greater than 0.
Default is volume with waste.
Optional. Leave blank if unknown. Cost cannot be negative.

Result dashboard

Bag count rounds up because concrete bags cannot be bought in partial bags.

Bags needed
Based on 80 lb bag yield and 10% waste.
147 bags
Base slab volume
2.96 cu yd
Order volume with waste
3.26 cu yd
Cubic feet
88.00 cu ft
Cubic meters
2.49 m³
Estimated cost
—
One bag covers
1.80 sq ft

This is an estimate. Confirm final quantity with your concrete supplier and check the exact yield printed on the bag.

Formula used

All measurements are converted to feet before the bag count is calculated.

Volume = Length × Width × Thickness × Number of slabs
Bags = Selected volume ÷ Bag yield