Concrete Bags for a 4x4 Slab - 40, 60, and 80 lb Counts
Estimate how many concrete bags you need for a 4x4 slab at common thicknesses, including 40 lb, 60 lb, and 80 lb bag counts with waste.
A 4x4 concrete slab is 16 square feet. At 4 inches thick, plan on about 18 bags of 40 lb concrete, 12 bags of 60 lb concrete, or 9 bags of 80 lb concrete before waste. With 10% waste, that becomes about 20 bags of 40 lb, 14 bags of 60 lb, or 10 bags of 80 lb concrete.
Use the Concrete Bag Calculator when you want to adjust thickness, bag size, waste factor, and bag price. This guide gives the quick 4x4 slab answer for small pads, equipment bases, and repair slabs.
Quick answer for a 4x4 slab
These estimates use common bag yields:
| Bag size | Common yield |
|---|---|
| 40 lb | 0.30 ft3 |
| 60 lb | 0.45 ft3 |
| 80 lb | 0.60 ft3 |
Approximate whole bags for a 4 ft by 4 ft slab:
| Thickness | 40 lb bags | 40 lb bags + 10% | 60 lb bags | 60 lb bags + 10% | 80 lb bags | 80 lb bags + 10% |
|---|---|---|---|---|---|---|
| 2 in | 9 | 10 | 6 | 7 | 5 | 5 |
| 3 in | 14 | 15 | 9 | 10 | 7 | 8 |
| 4 in | 18 | 20 | 12 | 14 | 9 | 10 |
| 5 in | 23 | 25 | 15 | 17 | 12 | 13 |
| 6 in | 27 | 30 | 18 | 20 | 14 | 15 |
All values are rounded up to whole bags. Check the yield printed on the bag you plan to buy, especially if you use a fast-setting or specialty mix.
Formula for a 4x4 slab
Start with slab volume:
cubic feet =
length ft x width ft
x thickness inches / 12
For a 4 ft by 4 ft slab at 4 inches:
4 x 4 x 4 / 12 = 5.33 ft3
Then divide by the bag yield:
bags needed = cubic feet / bag yield
Add waste before rounding up:
bags to buy =
round up(
bags needed x (1 + waste percentage)
)
For simple small slabs, 5% to 10% waste is a practical planning range. Use more if the base is uneven, the form depth varies, or the shape is irregular.
Example: 4x4 slab at 4 inches
Volume:
4 x 4 x 4 / 12 = 5.33 ft3
Using 40 lb bags:
5.33 / 0.30 = 17.78 bags
17.78 x 1.10 = 19.56
round up to 20 bags
Using 60 lb bags:
5.33 / 0.45 = 11.84 bags
11.84 x 1.10 = 13.02
round up to 14 bags
Using 80 lb bags:
5.33 / 0.60 = 8.89 bags
8.89 x 1.10 = 9.78
round up to 10 bags
For one-bag square-foot coverage by thickness, use the 40, 60, and 80 lb concrete bag coverage calculator.
Is bagged concrete practical for a 4x4 slab?
A 4x4 slab at 4 inches is about 0.20 cubic yards before waste:
5.33 / 27 = 0.20 yd3
This is usually a good size for bagged concrete. Ten 80 lb bags, fourteen 60 lb bags, or twenty 40 lb bags is still manageable for many DIY pours, especially with a small mixer or careful hand mixing.
If access is easy and you are pouring several pads at once, compare total cost in the Concrete Cost Calculator. For bigger slabs, compare delivery using the Ready-Mix vs Bags Calculator.
40 lb vs 60 lb vs 80 lb bags
For a 4x4 slab, the best bag size depends on lifting comfort and store price.
40 lb bags are easiest to lift, but they create the highest bag count. See the 40 lb Concrete Bag Calculator if handling weight is the limiting factor.
60 lb bags are a practical middle ground for small slabs. See the 60 lb Concrete Bag Calculator for yield and coverage details.
80 lb bags usually give the lowest bag count. See the 80 lb Concrete Bag Calculator before choosing them for a small pad.
For the next small-pad size, compare this with the Concrete Bags for a 6x6 Slab Guide. For larger square slabs, see the Concrete Bags for an 8x8 Slab Guide and the Concrete Bags for a 10x10 Slab Guide.
Buying checklist
- Confirm the slab is actually 4 ft by 4 ft after forms are set.
- Confirm the planned thickness at several points.
- Add waste before rounding to whole bags.
- Use the yield printed on the actual bag.
- Stage bags close to the pour area before mixing.
- Keep bags dry before use.
FAQ
How many 80 lb bags for a 4x4 slab at 4 inches?
A 4x4 slab at 4 inches needs about 9 bags of 80 lb concrete before waste or about 10 bags with a 10% waste factor.
How many 60 lb bags for a 4x4 slab at 4 inches?
A 4x4 slab at 4 inches needs about 12 bags of 60 lb concrete before waste or about 14 bags with a 10% waste factor.
How many 40 lb bags for a 4x4 slab at 4 inches?
A 4x4 slab at 4 inches needs about 18 bags of 40 lb concrete before waste or about 20 bags with a 10% waste factor.
How many cubic yards is a 4x4 slab at 4 inches?
A 4x4 slab at 4 inches is about 0.20 cubic yards before waste. With 10% waste, it is about 0.22 cubic yards.
Is a 4x4 slab too small for ready-mix?
Usually yes. A 4x4 slab is commonly small enough for bagged concrete. Ready-mix can still make sense if it is part of a larger pour or if you already have delivery scheduled.
Next step
Open the Concrete Bag Calculator to enter your actual slab thickness and bag size. For one-bag square-foot coverage tables, use the 40, 60, and 80 lb concrete bag coverage chart.
Quote planning next step
Turn this guide into a concrete buying check
Run the matching calculator, then compare ready-mix, bagged concrete, delivery fees, access needs, and quote gaps before you buy materials or approve a contractor number.