Compare the order you will actually place
The calculator converts length × width × depth into volume, adds your chosen allowance and rounds bags up. Bulk orders use the larger of your required volume and the supplier’s minimum; confirm any order increments directly.
Include delivery and handling
A 12-by-12 slab at 4 inches requires 48 cu ft before an allowance: 80 bags at 0.60 cu ft each. Those 80 lb bags weigh 6,400 lb in total. Vehicle capacity, site access and mixing time can matter as much as material price.
What to ask the supplier
Ask for the mix specification, minimum order, delivery and short-load fees, waiting-time charges, access requirements, and tax. Slab thickness here is a calculation input, not a structural recommendation.
Work through the bagged-versus-ready-mix decision
Show the original worked calculation
Volume = 10 × 20 × (4 ÷ 12) = 66.667 cu ft
= 66.667 ÷ 27 = 2.469 yd³
80 lb bags = 66.667 ÷ 0.60 = 111.111 → buy 112 bags
Cost @ $5.98 (HD 110180, 2026-08-27) = 112 × $5.98 = $669.76
60 lb bags = 66.667 ÷ 0.45 = 148.148 → buy 149 bags
Cost @ $4.48 (HD 110160) = 149 × $4.48 = $667.52
Optional 10% convention = 73.333 cu ft → 123 bags of 80 lbFormulas and manufacturer sources · Dated price references
Patio size comparison
These examples use a selected 4-inch depth with no extra allowance. Depth is an input for the arithmetic, not a design specification.
| Rectangle | Volume | 80 lb bags at 0.60 ft³ | 60 lb bags at 0.45 ft³ |
|---|---|---|---|
| 10 × 10 ft | 33.333 ft³ / 1.235 yd³ | 56 | 75 |
| 12 × 12 ft | 48 ft³ / 1.778 yd³ | 80 | 107 |
Bag weight changes handling and package rounding. Compare the cost of the whole order, including delivery and equipment, rather than assuming the larger bag is always cheaper.