Question 1

How many 80 lb bags of concrete do I need for a 10x10 slab?

Accepted Answer

A 10x10 foot slab at 4 inches thick requires approximately 12.3 cubic feet of concrete. With 10% waste factor, that is 13.6 cubic feet. At 0.60 cubic feet per 80 lb bag, you need 23 bags. Our Concrete Bag Calculator computes exact bag counts for all sizes (25 lb, 40 lb, 60 lb, 80 lb) and shows cost estimates instantly.

Question 2

What size concrete bag gives the best value?

Accepted Answer

80 lb bags consistently offer the best value per cubic foot - approximately $0.20 per cubic foot less than 40 lb bags. However, 80 lb bags are heavy to handle. For projects requiring more than 20 bags, consider 60 lb bags for a balance of value and manageability. Our calculator shows cost per cubic foot for every bag size.

Question 3

When should I use ready-mix concrete instead of bags?

Accepted Answer

Order ready-mix concrete when your project exceeds 1 cubic yard (27 cubic feet). At that volume, ready-mix is typically cheaper per cubic yard, faster to place, and produces a more consistent mix than hand-mixed bags. Our calculator alerts you when your project crosses the 1 cubic yard threshold.

Question 4

How deep should a concrete slab be?

Accepted Answer

Standard concrete slab thickness by application: 4 inches for patios and walkways, 4-6 inches for driveways, 6 inches for heavy vehicle traffic, 3.5 inches minimum for residential floors. Footings typically require 8-12 inches. Always check local building codes for structural applications.

Question 5

How much concrete do I need for a post hole?

Accepted Answer

Post hole concrete volume depends on hole diameter and depth. A 10 inch diameter hole 24 inches deep requires approximately 0.91 cubic feet or 2 bags of 60 lb concrete. A 12 inch hole 36 inches deep requires 2.36 cubic feet or 4 bags of 60 lb. Use our Concrete Bag Calculator with the Post Hole project type for exact counts.

Project	Dimensions	Cu Ft	60 lb Bags	80 lb Bags
Small Patio Slab	8x8 ft, 4" thick	18.1	41	31
Standard Patio	10x10 ft, 4" thick	28.2	63	47
Large Patio	12x12 ft, 4" thick	40.6	91	68
Garage Floor	20x20 ft, 4" thick	162.7	362	272
Sidewalk Section	4x8 ft, 4" thick	9.7	22	17
Deck Footing (x1)	12" dia, 42" deep	2.6	6	5
Fence Post (x1)	10" dia, 30" deep	1.0	3	2
Fence Post (x6)	10" dia, 30" deep	6.1	14	11
Mailbox Post	8" dia, 24" deep	0.5	2	1
Strip Footing	20 ft x 12" wide x 12" deep	22.0	49	37

Bag Size	Yield (cu ft)	Price (USD est.)	Cost per cu ft	Best For
25 lb	0.20 cu ft	~$5.50	~$27.50	Small repairs, single post holes
40 lb	0.30 cu ft	~$6.98	~$23.27	Small projects, easy handling
60 lb	0.45 cu ft	~$9.48	~$21.07	Medium projects, good balance
80 lb	0.60 cu ft	~$11.98	~$19.97	Best value, larger projects
20 kg (metric)	0.0085 m3	~$8.97 CAD	varies	Canadian metric projects
30 kg (metric)	0.0128 m3	~$12.97 CAD	varies	Larger Canadian projects

Volume	Recommendation	Reason
Under 0.5 cu yd	Bagged concrete	Easy, no minimum order, mix as needed
0.5 - 1.0 cu yd	Bagged concrete	Still manageable, avoids truck minimum charges
1.0 - 3.0 cu yd	Ready-mix or short-load	Ready-mix cheaper per yard, better consistency
Over 3.0 cu yd	Ready-mix truck	Significantly cheaper, faster, stronger result

Concrete Bag Calculator

Concrete Bags by Common Project (Quick Reference)

Concrete Bag Size Comparison

When to Use Ready-Mix vs Bagged Concrete