16x20 Concrete Slab, 4 Inches Thick
A 16 × 20 ft slab (320 sq ft) at 4 in thick takes about 4.35 cubic yards of concrete, with 10% extra for waste. For ready-mix, order 4.5 cu yd for the 16x20, about $690 – $920 delivered, short-load fee included. Bagged, the same 16x20 is 196 80 lb or 261 60 lb bags, about $1,305 – $1,827 for the concrete alone.
- Ready-mix order
- 4.5 cu yd
- Ready-mix cost
- $690 – $920
- 80 lb bags
- 196
- Bag cost
- $1,305 – $1,827
Materials only for a 16x20 at 4 in, from national price ranges as of 2026-09; not a live quote.
What a 16x20 slab usually carries
At 320 sq ft, a 16x20 slab is the floor of a large backyard workshop, a studio or a small pole building for a lawn tractor and tools, or a patio sized for a big family.
Sixteen feet is about the narrowest garage that holds a car plus a workbench along one wall, so some owners build a 16x20 as a compact one-car garage; if a car will park on it, think about 5 in.
A building this size will need a permit almost everywhere, and the inspector may want to see thickened edges or footings along the walls.
Before you pour the 16x20 at 4 in
- Find out from the building plans or the town whether the walls need a footing below the frost line or a thickened slab edge.
- Run water and power sleeves under the slab before the base goes down.
- Put a vapor barrier under the slab if the building will ever be heated or air-conditioned.
Full plan for a 16x20 slab, 4 in
- Area
- 320 sq ft
- Thickness
- 4 in
- Volume
- 4.35 cu yd
Bagged concrete estimate (DIY)
$1,615 – $2,331
Est. as of 2026-09 — not a live quote
Ready-mix delivered, incl. short-load fee (materials only)
$690 – $920
Est. as of 2026-09 — not a live quote
For a pour this size, ready-mix delivery is typically more practical than mixing bags by hand.
Shopping list
- Concrete mix (60 lb bags) Or 392 × 40 lb, 313 × 50 lb or 196 × 80 lb bags. 261 bags
- Ready-mix concrete Alternative to bagged mix; most suppliers have a 1 cu yd order minimum. 4.5 cu yd
- Compactable gravel sub-base 4 in compacted base beneath the slab. 5.33 tons
- 6x6 welded wire mesh Reinforcement for crack control; not a substitute for engineered rebar on structural slabs. 352 sq ft
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Buy bagged concrete
Pick up bagged mix and reinforcement from a hardware store for smaller pours.
View shopping listAssumptions
- Waste allowance: 10% applied to account for over-excavation and spillage.
- Approx. wet weight: 17,600 lb (8.8 tons).
- Prices are national-average retail/delivery ranges as of 2026-09, not live quotes.
- Ready-mix orders under 10 cu yd usually carry a short-load fee; the ready-mix range includes a flat $60-$110. Some suppliers charge per yard instead, so ask for the full fee schedule.
Bags or ready-mix for a 16x20 slab, 4 in?
4.35 cu yd for the 16x20 fits on one ready-mix truck (they carry about 8 to 10 cu yd). In bags the 16x20 would be 196 80 lb bags weighing 15,680 lb, so ready-mix is the practical choice. Under 10 cu yd most suppliers add a short-load fee, and the $690 – $920 range for the 16x20 includes one. On the 16x20, ready-mix comes out cheaper by about $761 at the middle of each range, and it saves mixing 196 bags.
Is 4 in thick enough for a 16x20 slab?
4 in is the usual thickness for a 16x20 patio, walkway, shed floor or equipment pad that carries foot traffic.
Control joints for a 16x20 slab at 4 in
A 16x20 slab at 4 in shrinks as it cures, and without joints it cracks wherever it chooses. The usual rule (ACI and PCA guidance) puts joints in a 16x20 at 4 in every 8 to 12 ft, 24 to 36 times the thickness, cut 1 in deep (a quarter of the thickness) as soon as the surface takes the saw without raveling, usually within the first day.
On the 16x20 at 4 in, a joint every 10 ft or less means 1 joint across the 20 ft side and 1 joint across the 16 ft side: 4 panels of about 10 × 8 ft and 36 ft of saw cut.
How much a 16x20 slab 4 in thick weighs
Wet concrete weighs about 150 lb per cubic foot, so the 16x20 pour is about 17,600 lb (8.8 tons). As bags, the 16x20 is 196 80 lb bags, 15,680 lb in all: about 11 trips in a pickup carrying 1,500 lb a load. Nobody hauls 15,680 lb of bags for a 16x20 in a pickup; it comes by ready-mix truck or as pallets on a delivery truck.
The 16x20 at 4 in against nearby sizes
Every row uses the same 10% waste and prices as the 16x20 at 4 in; costs are for the concrete only.
| Slab | Cu yd | 60 lb bags | 80 lb bags | Ready-mix order | Bags cost | Ready-mix cost |
|---|---|---|---|---|---|---|
| 12x24 slab, 4 in | 3.91 | 235 | 176 | 4 cu yd | $1,175 – $1,645 | $620 – $830 |
| 16x20 slab, 4 in (this page) | 4.35 | 261 | 196 | 4.5 cu yd | $1,305 – $1,827 | $690 – $920 |
| 12x30 slab, 4 in | 4.89 | 294 | 220 | 5 cu yd | $1,470 – $2,058 | $760 – $1,010 |
Questions about a 16x20 slab, 4 in
How many bags of concrete for a 16x20 slab 4 inches thick?
Plan on 117.3 cubic feet for the 16x20, which is 196 80 lb bags, 261 60 lb bags, 313 50 lb or 392 40 lb bags once 10% waste is in.
How many yards of concrete for a 16x20 slab 4 inches thick?
The 16x20 measures out at 3.95 cubic yards, or 4.35 with 10% for waste. Order 4.5 cu yd for the 16x20, since ready-mix is sold in quarter yards with a 1 yard minimum at most plants.
How much does a 16x20 concrete slab 4 inches thick cost?
Concrete alone for the 16x20 runs about $690 – $920 for 4.5 cu yd of ready-mix delivered, short-load fee included, or $1,305 – $1,827 for 261 60 lb bags. Add a 4 in gravel base and wire mesh and the bagged 16x20 plan comes to $1,615 – $2,331. Labor, forms and finishing for a 16x20 at 4 in come on top of these national ranges (as of 2026-09), which are not quotes.
How much does a 16x20 concrete slab 4 inches thick weigh?
About 17,600 lb (8.8 tons) of wet concrete for the 16x20, at 150 lb per cubic foot. The 196 80 lb bags for a 16x20 weigh 15,680 lb: about 11 trips in a pickup carrying 1,500 lb a load.
Where do control joints go on a 16x20 slab 4 inches thick?
On a 16x20 at 4 in, every 8 to 12 ft (24 to 36 times the thickness), sawn 1 in deep. On the 16x20 at 4 in, a joint every 10 ft or less means 1 joint across the 20 ft side and 1 joint across the 16 ft side: 4 panels of about 10 × 8 ft and 36 ft of saw cut.
Limitations
The 16x20 figures at 4 in are material estimates and typical price ranges, not a quote or a structural design. Confirm that 4 in, the reinforcement and the joint layout suit your soil, loads and local code for a 16x20 slab with a qualified professional.