How Many Bags of Concrete for a 4x4 Slab?
A 4×4 slab at a standard 4 inches thick needs 9 bags of 80 lb concrete (or 12 bags of 60 lb), with a 5% waste factor included. That's 5.3 cu ft total — small enough to pour solo in one Saturday with no mixer rental, no helpers, and no short-load fees.
slab Dimensions
Typical finished slab: $6–12 / sq.ft (labor + materials)
Total Material Needed
Recommended For This Job
The Quick Answer: 4x4 Concrete Slab Bag Count
| Thickness | Cubic Feet | 80 lb Bags | 60 lb Bags |
|---|---|---|---|
| 3 inches | 4.0 | 7 | 10 |
| 4 inches (standard) | 5.3 | 9 | 12 |
| 5 inches | 6.7 | 12 | 16 |
| 6 inches (heavy-duty) | 8.0 | 14 | 19 |
* Includes 5% waste factor. 80 lb bag yield: 0.60 cu ft. 60 lb bag yield: 0.45 cu ft.
How We Calculate Bags for a 4x4 Slab
4 ft × 4 ft × 0.333 ft (4 in) = 5.33 cubic feet
5.33 × 1.05 (5% waste) = 5.6 cubic feet
5.6 ÷ 0.60 (80 lb bag yield) = 9 bags (rounded up)
A 4x4 slab is the most DIY-friendly concrete project there is — just under 0.2 cubic yards. No need to rent a mixer, no short-load fees to worry about, and one person can finish the whole pour in a single afternoon.
Common Uses for a 4x4 Concrete Slab
- Central AC condenser pad: Fits residential units up to 5 tons. 4 inches thick is plenty; add a 6-mil vapor barrier underneath to keep condensation off the compressor.
- BBQ grill or outdoor kitchen base: A 4x4 slab handles any freestanding grill comfortably. Add rebar if you plan to anchor a permanent outdoor kitchen cabinet.
- Small hot tub or spa (2-person portable): Fine for portable tubs under 68×68 inches. For standard 4-person tubs you want 6x6 or larger at 6 inches thick — a filled tub can exceed 5,000 lb.
- Generator pad: Standby generators (Generac, Kohler 14–22 kW) typically ship with a composite pad, but a 4x4 concrete slab is sturdier and looks cleaner.
- Trash can / recycle bin corral: Keeps plastic bins off the dirt, stops them blowing around in storms. 3 inches thick is enough.
- Shed / small prefab storage: Only works for sheds up to 4×4 or 4×6. For larger sheds see our 10×10 or 12×12 calculators.
One-Saturday DIY Timeline (9 Bags, Solo)
A 4×4 slab is the only concrete project where realistic 1-day, 1-person DIY math works without compromise. Here is the hour-by-hour plan most homeowners follow, assuming forms and gravel base were prepped the day before.
Re-check form level + dampen gravel base
Sub-base must be moist (not muddy) so the slab does not lose water to dry gravel during cure. Spray with garden hose, walk away for 10 minutes.
Stage 9 bags + tools next to forms
Wheelbarrow, hoe, mixing tub, 2-gallon water jug, screed board (5-ft 2×4), darby float, edging tool, broom for finish.
Mix and pour batch 1 (3 bags)
1.5 quarts water per 80 lb bag in the wheelbarrow. Hoe to oatmeal consistency, dump into the form starting at the far corner.
Mix and pour batch 2 (3 bags)
Continue from where batch 1 ended. Push the wet edge of batch 1 into batch 2 to eliminate the cold joint.
Mix and pour batch 3 (3 bags)
Final 3 bags fills the form. Aim to finish all pouring by 10:30 — concrete starts setting fast on warm days.
Screed level with the 2×4
Saw back and forth across the form, dragging excess concrete off the high side. One pass should be enough on a 4×4.
Bull-float (or darby) the surface
Floats out the screed marks. Stop the moment water starts pooling — over-floating brings cement slurry to the top and weakens the surface.
Lunch / wait for bleed water to evaporate
You CANNOT trowel or broom-finish until the surface dampness is gone. Usually 1–2 hours depending on weather.
Edging tool + control joint
Run the edging tool along the form to round the slab edges. Cut a single control joint across the middle, 1 inch deep with a grooving tool.
Broom finish for traction
Pull a stiff push broom across the surface in straight lines. Stops it from being slippery when wet.
Cover with plastic sheeting
6-mil plastic over the slab traps moisture for the first 24 hours. Critical step — concrete that dries in the sun cracks. Mist daily for 3 days, then remove plastic.
Done. Foot traffic in 24 hr, full strength at 28 days
Total elapsed time: 8 hours. Total active labor: 4–5 hours. AC unit can sit on the pad after 7 days.
4×4 as an AC Condenser Pad: Code-Compliant Spec
A central AC condenser is the most common reason people search for "how many bags for a 4×4 slab." Most residential condensers (2–5 ton, Carrier / Trane / Goodman / Lennox) have a 30-inch to 36-inch square footprint, so a 48-inch (4 ft) pad gives 6–9 inches of clearance on each side — enough to meet manufacturer install specs and the 12-inch service clearance most local codes require.
Spec checklist for an AC pad
- Thickness: 4 inches is sufficient for any residential condenser up to 5 tons (~250 lb dry, ~350 lb running). 9 bags of 80 lb.
- Distance from house: Minimum 12 inches from siding for service access (most jurisdictions). Some manufacturers spec 18–24 inches for rear-discharge units.
- Levelness: Within 1/8 inch across the pad. An out-of-level condenser stresses refrigerant lines and shortens compressor life. Re-check with a 4-ft level after the screed pass.
- Drainage slope: 1/8 inch per foot away from the house foundation. Prevents condensate runoff from soaking the foundation wall.
- Vibration isolation: Set the condenser on rubber pads ($15–$25, 4 corners) on top of the slab — not directly on concrete. Reduces compressor noise transferred into the house wall.
- Anchoring (hurricane / high-wind zones): Two 1/4"×3" concrete anchors through the unit's base feet. Drill after slab cures 7+ days.
Code shortcut: Most US jurisdictions reference the manufacturer's install manual, which typically requires a level non-combustible pad with the unit footprint plus 6" clearance on the service side. A 4×4 concrete slab clears all common requirements. Composite condenser pads (Diversitech, etc.) are also code-compliant but tend to settle and tilt within 3–5 years on most soils — concrete lasts the life of the house.
DIY Tips for Pouring a 4x4 Slab
- Skip the mixer rental: Nine 80 lb bags is about 1–2 hours of mixing in a wheelbarrow. A rental mixer would cost more than the concrete itself for this size.
- Mix 3 bags at a time: A standard wheelbarrow handles 3 bags comfortably. Pour, screed level, then start the next batch while the first cures slightly.
- Set forms 3.5 inches above grade: For a 4-inch finished slab, excavate 4 inches + add 3.5 inches of gravel base, so the form top sits 3.5 inches above the surrounding ground.
- Buy 10 bags, not 9: The extra bag is insurance. Unused bags return cleanly to Home Depot or Lowe's as long as they are dry and intact.
- Screed in one pass: A 4×4 area is small enough that one person can screed from one side to the other with a straight 2×4 without stopping.
Frequently Asked Questions
How many 80 lb bags of concrete do I need for a 4x4 slab?
A 4x4 slab at 4 inches thick needs 9 bags of 80 lb concrete (with 5% waste factor). The raw math is 8.88 bags — always round up to 9.
How many 60 lb bags of concrete for a 4x4 slab?
You will need 12 bags of 60 lb concrete for a 4x4 slab at 4 inches thick. 60 lb bags yield 0.45 cu ft each, so you need more of them, but they are easier to carry.
Is a 4x4 slab big enough for an AC unit?
Yes. Most residential central AC condensers have a footprint of 30×30 to 36×36 inches, so a 4x4 slab (48×48 inches) gives the required 2–3 inches of clearance on each side.
Is a 4x4 slab big enough for a hot tub?
Only for the smallest 2-person portable tubs. For a standard 4-person hot tub, use at least 6x6 at 6 inches thick.
Can one person pour a 4x4 slab in a day?
Yes. A 4x4 slab is the easiest DIY concrete project — 9 bags of 80 lb takes 1 to 2 hours of mixing. No mixer rental needed.
How much does a 4x4 concrete slab cost?
Materials cost about $60 to $80 (9 bags at $6.48 to $8.47 each). Contractor pricing is typically $100 to $200 total due to minimum-charge fees.