River rock calculator
A bed 20 ft long and 4 ft wide, covered 3 in deep, takes 0.74 cubic yards of river rock, about 0.96 tons.
What river rock weighs
River rock is rounded stone, sold in sizes from under an inch to several inches across. The U.S. Environmental Protection Agency's conversion table lists loose rock at 2,570 lb per cubic yard and large stone at 100 lb per cubic foot (2,700 lb per yard). The calculator uses 2,600 lb, which is 1.30 tons per yard. Large stones leave bigger gaps between them, so the weight of a yard varies with the size you buy. If your supplier gives a weight per yard, choose "Other" and enter it.
Area: 20 ft × 4 ft = 80 sq ft
80 sq ft × 3 in = 20 cu ft ÷ 27 = 0.74 cu yd
0.74 cu yd × 2,600 lb per loose cu yd ÷ 2,000 = 0.96 tons
Choosing a depth
The layer has to be deeper than the stones are wide, or bare ground shows between them. Small river rock can cover at 2 in. For larger stones, a common rule of thumb is a layer about twice as deep as the stones are wide. A landscape fabric under the rock slows weeds and keeps the stone from sinking into soft soil.
| Depth | Sq ft per cu yd | Sq ft per ton | Cu yd per 100 sq ft |
|---|---|---|---|
| 2 in | 162 | 125 | 0.62 |
| 3 in | 108 | 83 | 0.93 |
| 4 in | 81 | 62 | 1.23 |
| 6 in | 54 | 42 | 1.85 |
Dry creek beds
A dry creek bed is a shallow channel lined with rock. Measure its length along the middle, its average width across the top, and the average depth of rock. A channel 30 ft long and 3 ft wide with rock 6 in deep takes 1.67 cubic yards, about 2.17 tons. Creek beds usually mix sizes, with larger boulders along the edges; count boulders separately, since a few large stones add weight quickly.
Sources
- Standard Volume-to-Weight Conversion Factors, U.S. Environmental Protection Agency, March 2016. Loose weights of gravel, rock, sand, sandy loam soil and shredded wood chips.
- How Much Compost, Soil or Mulch Do I Need to Purchase?, Texas AgriLife Extension Service, Travis County, February 2010. Square feet times depth in inches, divided by 324, gives cubic yards.