How Many Bags of Concrete for a Slab? (50, 60, 80 lb Tables)

How Many Bags of Concrete for a Slab — Direct Answer

For a standard 4-inch slab, you need 1 × 80-lb bag per 0.6 sq ft, or one 60-lb bag per 0.45 sq ft. A 10×10 slab at 4" thick requires 56 bags of 80-lb, 74 bags of 60-lb, or 111 bags of 40-lb concrete. Add 10% for waste.

→ Calculate exact bag counts with our concrete slab calculator

How to Calculate Bags of Concrete for a Slab

Bag count depends on slab volume, bag yield, and slab thickness. The math is straightforward when you work in cubic feet.

Volume (cu ft) = Length ft × Width ft × (Thickness in ÷ 12)
Bags = Volume × 1.10 ÷ Bag Yield

Where:

• 1.10 = 10% waste factor for spillage and form absorption
• Bag Yield = cubic feet produced by one bag

How to measure slab square footage and thickness

Slabs are measured in square feet (area) and inches (thickness). Common thicknesses:

Slab Type	Typical Thickness
Walkway	3–4 inches
Patio	4 inches
Garage floor	4–5 inches
Driveway	4–6 inches
Foundation	6–12 inches

How to convert to bags

Standard bag yields from US manufacturers:

Bag Size	Yield (cu ft)	Bags per Yard
40 lb	0.30	90
50 lb	0.375	72
60 lb	0.45	60
80 lb	0.60	45

How to apply the formula to real slabs

Example: 12×12 patio at 4" thick

• Volume = 12 × 12 × (4 ÷ 12) = 48 cu ft
• Add 10% waste = 52.8 cu ft
• Bags (80 lb) = 52.8 ÷ 0.6 = 88 bags
• Bags (60 lb) = 52.8 ÷ 0.45 = 118 bags
• Bags (40 lb) = 52.8 ÷ 0.30 = 176 bags

Concrete Bag Count Tables by Slab Size

4-inch thick slabs

Slab Size	Cu Ft	40 lb	60 lb	80 lb
4×4	5.3	20	13	10
6×6	12.0	45	30	22
8×8	21.3	79	53	39
10×10	33.3	123	82	61
12×12	48.0	176	118	88
16×16	85.3	313	209	156
20×20	133.3	490	327	245

6-inch thick slabs

Slab Size	Cu Ft	40 lb	60 lb	80 lb
4×4	8.0	30	20	15
6×6	18.0	66	44	33
8×8	32.0	118	79	59
10×10	50.0	184	122	92
12×12	72.0	264	176	132
16×16	128.0	470	313	235

Thickness vs bag count (10×10 slab)

Thickness	Cu Ft	40 lb	60 lb	80 lb
3"	25.0	92	61	46
4"	33.3	123	82	61
5"	41.7	153	102	77
6"	50.0	184	122	92

Common Bags-of-Concrete-for-Slab Mistakes

Mistake 1: Using the wrong bag yield

A generic "40 lb bag" isn't always 0.30 cu ft. Some brands yield 0.29, some 0.32.

Fix: Read the bag label. Look for "YIELD" or "COVERAGE". Use the exact number.

Mistake 2: Not adding waste

Concrete doesn't return. If you mix 40 bags and need 42, you're short.

Fix: Always add 10% for slabs, 15% for irregular shapes or elevated pours.

Mistake 3: Mixing too much at once

Premix sets in 30 minutes. If you mix 20 bags, 15 will harden before you finish pouring.

Fix: Buy extra bags, but mix in batches of 5–10. Use a wheelbarrow and hoe for consistency.

When to Use Bagged vs Ready-Mix Concrete

Use bagged concrete when

• Total volume < 1 cubic yard (27 cu ft)
• Access is limited for a truck
• You need 1–4 fence posts or small pads
• You want to work at your own pace

Use ready-mix concrete when

• Total volume > 1 cubic yard
• You need a professional finish
• Time is critical (curing starts at pour)
• The slab is over 4" thick

Cost comparison

Bagged	Ready-Mix
$6–$9 per 80-lb bag	$150–$200 per yard
~$360–$450 per yard	2–3× cheaper per yard
No minimum order	3-yard minimum + short-load fee

Concrete Bag Calculator FAQ

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

A 10×10 slab at 4" thick needs 61 bags of 80-lb concrete. At 6" thick, it needs 92 bags.

How many bags of concrete are in a yard?

45 bags of 80-lb, 60 bags of 60-lb, or 90 bags of 40-lb premix make 1 cubic yard.

How many bags of concrete do I need for a 12x12 slab?

A 12×12 slab at 4" thick needs 88 bags of 80-lb concrete, or 118 bags of 60-lb.

How much does 1 bag of concrete cover?

An 80-lb bag covers 0.6 cu ft, or about 1.8 sq ft at 4" thick. A 60-lb bag covers 1.35 sq ft at 4" thick.

Can I pour a slab with bagged concrete?

Yes, for slabs up to 1 cubic yard (27 cu ft). Larger slabs need ready-mix delivery for proper curing and consistency.

Next Steps for Your Slab Project

• Concrete Slab Calculator — Exact bag counts
• Cement Bag Calculator — Cement-only batching
• Concrete Footing Calculator — Footing bags
• Bags of Concrete Per Yard — Compare yields
• Concrete Slab Calculator Guide — Full volume walkthrough

---

Last updated October 2026. Verify bag yields on your specific product label — manufacturers vary slightly.