Bags of River Rock for a 8x18 Patio
How many bags of river rock for a 8x18 patio: at 3 inches deep you need about 36.0 cubic feet, which is 72 bags of the common 0.5 cubic foot size. If your store sells river rock in 50-pound bags instead, figure about 72 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 | 12.0 | 24 | 24 |
| 2 in | 24.0 | 48 | 48 |
| 3 in | 36.0 | 72 | 72 |
| 4 in | 48.0 | 96 | 96 |
How to figure it
- Area: 8 × 18 = 144 sq ft.
- Volume: 144 × (3 ÷ 12) = 36.0 cu ft.
- Bags: 36.0 ÷ 0.5 = 72 bags (round up).
Bags or bulk?
A cubic yard is 27 cubic feet, so 36.0 cubic feet is 1.33 yards, about 1.8 tons. At this size, a bulk delivery usually beats a cart full of bags once you count trips. Compare the bag price × 72 against a bulk quote for 2.0 tons delivered.
About river rock
River rock is smooth, water-worn stone sold in sizes from about 3/4 inch to several inches. Larger sizes cover fewer square feet per ton at the same depth because the voids between stones are bigger.
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
Best suited to:
- 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 10x20 area at 3 inches takes about 2.5 tons.
- Weight used here: about 1.35 tons per cubic yard.
Common estimating mistakes
- Assuming every supplier uses the same weight. Two yards selling the same product name can quote different tons per yard.
- Measuring only the main rectangle. Aprons, turnouts and curved edges add real square footage.
- Ignoring the base. A thin surface layer over soft soil fails early no matter how much material is on top.
- Skipping drainage. Water sitting under any surface softens the base and leads to ruts and potholes.
Questions people ask
How many bags of river rock for a 8x18 patio?
About 72 bags of 0.5 cubic feet at 3 inches deep.
How many 50 lb bags of river rock for 8x18?
About 72 bags at 3 inches.
How many 0.5 cubic foot bags are in a cubic yard?
54 bags.
How many cubic feet is a 8x18 patio at 3 inches?
About 36.0 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 8x14 Patio
- Bags of River Rock for a 8x16 Patio
As an Amazon Associate, AsphaltTons.com earns from qualifying purchases. Product links below are sponsored.