How Much River Rock for a 20x18 Patio?
How much river rock for a 20x18 patio is a quick volume problem. 360 square feet at 3 inches comes to 3.33 cubic yards. River rock usually weighs about 1.25 to 1.45 tons per cubic yard, so plan on roughly 4.5 tons.
Volume and tonnage calculator →The math for a 20x18 patio
- Area: 20 × 18 = 360 sq ft.
- Depth in feet: 3 ÷ 12 = 0.250 ft.
- Cubic feet: 360 × 0.250 = 90.0 cu ft.
- Cubic yards: ÷ 27 = 3.33 yd³.
- Tons: × 1.35 = 4.5 tons.
The volume and tonnage calculator does this for any size.
River rock needed by depth
| Depth | Cubic yards | Tons (approx.) | Tons +10% |
|---|---|---|---|
| 2 in | 2.22 | 3.0 | 3.3 |
| 3 in | 3.33 | 4.5 | 5.0 |
| 4 in | 4.44 | 6.0 | 6.6 |
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. Weight per yard is a planning number; the scale ticket at the yard is the real one.
Preparing the patio
Remove sod, level the area with a slight slope away from the house, and lay landscape fabric if weeds are a concern. Edging keeps loose material inside the patio footprint. This patio sees foot traffic and furniture, so match the depth to that load rather than to the minimum.
Ordering tips
- Round up. Compaction and uneven ground eat material. Adding about 10 percent is common.
- Delivery size. 5.0 tons fits in a single typical dump truck load; small loads may carry a delivery fee. See how many tons of gravel in a dump truck.
- Bulk vs bags. At this size bulk delivery is usually the practical choice.
- Where it drops. Have the truck dump as close to the patio as firm ground allows.
When to choose river rock
Works well for:
- 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 4 inches takes about 7.5 tons.
- Weight used here: about 1.35 tons per cubic yard.
Common estimating mistakes
- Forgetting that compaction shrinks loose material. A loose 4-inch spread of a dense-graded stone may finish closer to 3 inches after rolling.
- 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.
- Ordering exactly the math. Uneven ground and spillage nearly always need a little more than the flat calculation.
Questions people ask
How many tons of river rock for a 20x18 patio?
About 4.5 tons at 3 inches deep, or 5.0 tons with 10 percent extra.
How many cubic yards is a 20x18 patio at 3 inches?
About 3.33 cubic yards.
How much does a cubic yard of river rock weigh?
Usually around 1.25 to 1.45 tons, depending on stone size, fines and moisture.
How deep should river rock be for a patio?
The table above shows 2 to 4 inches. Shallower depths suit top dressing; deeper depths suit new installs and heavier use.
How many square feet is 20x18?
360 square feet.
Related guides
- How Much Does a Ton of River Rock Cover?
- Tons to Cubic Yards for Gravel: Conversion Chart
- How Many Tons of Gravel in a Dump Truck? Loads and Coverage
- How Much Does a Ton of Gravel Cover? Depth Chart
- How Much River Rock for a 20x14 Patio?
- How Much River Rock for a 20x16 Patio?
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