How it works
Estimate the concrete volume and bag count for a rectangular slab.
Enter the slab length and width in feet and the depth in inches. The calculator computes volume in cubic feet and cubic yards and estimates the number of 80 lb and 60 lb bags.
Formula
Volume (ft³) = length × width × depth ÷ 12; cubic yards = ft³ ÷ 27.
L- Length (ft)
W- Width (ft)
D- Depth (in)
Examples
- 10 ft × 10 ft slab, 4 in deepLength 10 · width 10 · depth 4 in33.33 ft³ ≈ 1.23 yd³ · ≈ 56 × 80 lb bags or 75 × 60 lb bags
Frequently asked questions
How many bags per cubic yard?
Approximately 45 × 80 lb bags or 60 × 60 lb bags make one cubic yard, depending on the manufacturer.
Should I order extra?
Yes — add about 5–10% for spillage, uneven ground, and form variations.
How to read the result
Cubic yards is the standard ordering unit for ready-mix concrete. Bag counts are rounded up to whole bags.
Limitations
Assumes a flat, rectangular slab with uniform depth. A typical 80 lb bag yields ≈ 0.6 ft³ and a 60 lb bag ≈ 0.45 ft³; check the manufacturer for exact yield.
Source: Rectangular volume formula; bag yields are typical manufacturer values.