Bags of River Rock for a 12x18 Patio
How many bags of river rock for a 12x18 patio: at 3 inches deep you need about 54.0 cubic feet, which is 108 bags of the common 0.5 cubic foot size. If your store sells river rock in 50-pound bags instead, figure about 108 bags, since river rock weighs roughly 100 pounds per cubic foot.
Volume and tonnage calculator →Bag count by depth
| Depth | Cubic feet | 0.5 cu ft bags | 50 lb bags (approx.) |
|---|---|---|---|
| 1 in | 18.0 | 36 | 36 |
| 2 in | 36.0 | 72 | 72 |
| 3 in | 54.0 | 108 | 108 |
| 4 in | 72.0 | 144 | 144 |
How to figure it
- Area: 12 × 18 = 216 sq ft.
- Volume: 216 × (3 ÷ 12) = 54.0 cu ft.
- Bags: 54.0 ÷ 0.5 = 108 bags (round up).
Bags or bulk?
A cubic yard is 27 cubic feet, so 54.0 cubic feet is 2.00 yards, about 2.7 tons. Past about a yard, bulk is usually less work and often less money. Compare the bag price × 108 against a bulk quote for 3.0 tons delivered.
About river rock
River rock is mostly decorative and for drainage beds. It is not meant to be driven on and tends to roll if used as a walking surface.
Laying it down for a patio
- Dig and level. Remove sod and set the base slightly below the surrounding grade.
- Edge it. Steel, plastic or stone edging keeps material in place.
- Spread in layers. Rake to depth, then rake smooth; rounded stone will not compact.
- Buy a few extra. Grab 5 to 10 percent more bags for settling and touch-ups.
The volume and tonnage calculator handles other sizes and depths.
Where river rock fits
Good uses:
- Dry creek beds and drainage swales
- Decorative borders and planting beds
- Around downspouts to stop splash erosion
Think twice for:
- Walking surfaces
- Driveways
- Bases under slabs or pavers
Quick reference numbers
- Per inch over 100 sq ft: about 0.42 tons of river rock (0.31 cubic yards).
- Per inch over 1,000 sq ft: about 4.2 tons.
- Another size for comparison: a 15x30 area at 3 inches takes about 5.6 tons.
- Weight used here: about 1.35 tons per cubic yard.
Where estimates go wrong
- Mixing up cubic yards and tons. Yards are volume, tons are weight; convert with the product’s weight per yard.
- Assuming every supplier uses the same weight. Two yards selling the same product name can quote different tons per yard.
- Skipping drainage. Water sitting under any surface softens the base and leads to ruts and potholes.
- Using inches as if they were feet. Depth has to be divided by 12 before you multiply; skipping that step inflates the order twelvefold.
Questions people ask
How many bags of river rock for a 12x18 patio?
About 108 bags of 0.5 cubic feet at 3 inches deep.
How many 50 lb bags of river rock for 12x18?
About 108 bags at 3 inches.
How many 0.5 cubic foot bags are in a cubic yard?
54 bags.
How many cubic feet is a 12x18 patio at 3 inches?
About 54.0 cubic feet.
When does bulk make more sense?
Usually once the job passes about a cubic yard, or when you would need more than a few car trips.
Related guides
- How Much Does a Ton of River Rock Cover?
- Tons to Cubic Yards for Gravel: Conversion Chart
- How Much Does a Ton of Gravel Cover? Depth Chart
- Bags of River Rock for a 12x14 Patio
- Bags of River Rock for a 12x16 Patio
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