How many bags of concrete for a 4×4 slab?
A 4 × 4 ft pad 4 inches thick is 5.3 cubic feet of concrete (0.2 cubic yards). With 10% extra that is 10 bags of 80 lb mix or 14 bags of 60 lb.
How to work it out
- 4 ft × 4 ft = 16 sq ft
- 16 sq ft × 4 in ÷ 12 = 5.33 cu ft ÷ 27 = 0.2 cu yd
- + 10% extra = 0.22 cu yd = 5.87 cu ft
- 5.87 cu ft ÷ 0.6 cu ft per 80 lb bag = 10 bags
A 4 × 4 pad is the go-to base for an AC condenser, a generator, a trash-can corner or a small grill. It is squarely a bag job: one person with a tub and a hoe can mix and place it in an afternoon.
Adjust for your project
More options: Extra · Price
- Or bags of mix (incl. extra)
- 10 bags · 80 lb bag
- Concrete before the extra
- 0.2 cu yd (5.33 cu ft)
- Slab area
- 16 sq ft
- Weight of the concrete (≈ 145 lb/cu ft)
- 773 lb (0 tons)
- Total to buy counts this as bags. Switch “How will you buy it?” to ready-mix truck if you are ordering a delivery.
4×4 pad by thickness (10% extra included)
| Thickness | Or bags of mix (incl. extra) | Concrete to order | Weight of the concrete (≈ 145 lb/cu ft) |
|---|---|---|---|
| 3.5 in | 9 bags | 0.19 cu yd | 677 lb |
| 4 in | 10 bags | 0.22 cu yd | 773 lb |
| 5 in | 13 bags | 0.27 cu yd | 967 lb |
| 6 in | 15 bags | 0.33 cu yd | 1,160 lb |
80 lb or 60 lb bags for a 4×4?
Ten 80 lb bags weigh 800 lb; fourteen 60 lb bags weigh 840 lb. You are lifting about the same total either way, so pick the size you can carry comfortably — the 60s mean four more bags to open and mix, but each lift is lighter. With no extra at all the pad takes 8.9 of the 80 lb bags, so nine is cutting it fine; buy ten and return an unopened one if it isn’t needed.
Mix two bags at a time in a tub with roughly 6 pints of water per 80 lb bag to start, adding a little more only until the mix is stiff but workable. Place it, screed it with a straight 2×4 riding on the forms, and float it before the bleed water appears.
Pad details
For equipment, check the maker’s installation guide: many outdoor units want the pad a few inches above grade and a little larger than the unit’s footprint, and some specify a particular pad. Set the forms on compacted gravel, and slope the top very slightly so water runs off. Four feet is short enough that a control joint isn’t needed. If the pad is 3½ in deep (a 2×4 form), you need 9 bags of 80 lb with the 10% extra. For a bigger pad, how many bags of concrete for an 8×8 slab runs the same numbers, and a patio is on how much concrete for a 10×10 slab.
Different size? Use the full Concrete Calculator.
What you’ll need
- Mortar and concrete mixing tubBudget price
A wide, shallow tub for one or two bags at a time — easier to clean and to pull a hoe through than a wheelbarrow.
See options on Amazon (opens in a new tab) - Mortar hoeBudget price
The holes in the blade pull water through dry mix, so bagged concrete and mortar mix evenly without dry pockets.
See options on Amazon (opens in a new tab) - Magnesium hand floatBudget price
Closes the surface and pushes stones down after screeding, and prepares the slab for a broom or trowel finish.
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Frequently asked questions
How many 60 lb bags of concrete for a 4×4 slab?
14 bags of 60 lb for a 4 inch pad with 10% extra.
How many bags of concrete for a 4×4 pad 6 inches thick?
15 bags of 80 lb with 10% extra (0.33 cubic yards).
How many 50 lb bags of concrete for a 4×4 slab?
About 16 bags of 50 lb at 4 inches, including 10% extra.
Other common sizes
- How much concrete for a 10×10 slab — 1.36 cu yd with 10% extra (62 bags of 80 lb)
- How much concrete for a 12×12 slab — 1.96 cu yd with 10% extra (order 2 yd)
- How much concrete for a 20×20 slab — 5.43 cu yd with 10% extra at 4 in
- How many yards of concrete for a 24×24 slab — 7.82 cu yd with 10% extra at 4 in
- How much concrete for a 30×40 slab — 16.3 cu yd with 10% extra at 4 in
- How many bags of concrete for an 8×8 slab — 40 bags of 80 lb, 4 in thick
- How much concrete for a 10×12 shed — 1.63 cu yd with 10% extra; about 2 cu yd with a thickened edge
Sources
- Quikrete Concrete Mix (No. 1101) data sheet (opens in a new tab) — Yields: 40 lb ≈ 0.30, 50 lb ≈ 0.375, 60 lb ≈ 0.45, 80 lb ≈ 0.60, 90 lb ≈ 0.675 cu ft; unit weight ≈ 140 lb/cu ft; for pours 2 in thick or more; 6–9 pints of water per 80 lb bag; control joints every 6–8 ft; cure 5 days at 70 °F or above, 7 days at 50–70 °F; protect from freezing for 48 hours.
- NRMCA Concrete in Practice 31 — Ordering Ready Mixed Concrete (opens in a new tab) — Truck mixers carry 8 to 12 cubic yards (about 6 to 9 m³); order 4–10% more than the plan estimate; a loaded truck weighs about 80,000 lb; fresh concrete can cause severe chemical burns.
- NRMCA Concrete in Practice 2 — Scaling Concrete Surfaces (opens in a new tab) — Order air-entrained concrete (about 6% air) for exterior slabs exposed to freezing and de-icers; avoid de-icing chemicals in the first winter.
- Iowa DOT Instructional Memorandum 340 — Weight per cubic foot, yield and air content of concrete (opens in a new tab) — Normal-weight concrete is typically 140–150 lb per cu ft at 5 to 8 percent air.
- OSHA 3351 — Preventing Skin Problems from Working with Portland Cement (opens in a new tab) — Wet portland cement can cause caustic burns that may not hurt at first and in severe cases reach the bone.
- NIST Handbook 44, Appendix C — General Tables of Units of Measurement (opens in a new tab) — 1 cubic yard = 27 cubic feet; 1 cubic foot = 1,728 cubic inches.