The River Rock Calculator calculates volume, short tons, bags and loads from your measurements. Use the table below to understand how depth changes the result before selecting a product.
Measure the bed without counting overlap#
Sketch the bed and divide it into rectangles, triangles or circles. Multiply each rectangle's length by width; use half the product of base and perpendicular height for triangles. Add the separate areas and subtract permanent features that will not receive rock. Do not count the same corner in two shapes.
For a curved bed, repeated width measurements can help build a preliminary area estimate. Check the result against the actual border before ordering. A small area error applies to the full installation depth.
Keep units consistent. A width measured in inches must be converted to feet before multiplying by a length in feet. The NIST volume reference explains cubic units; the conversion here uses 12 inches per foot and 27 cubic feet per cubic yard.
Coverage by depth: hypothetical volume table#
These are geometric examples, not recommended installation depths. Select depth based on stone size, supplier guidance and the project's intended function. No density or allowance is included.
| Bed area | At 2 in | At 3 in | At 4 in |
|---|---|---|---|
| 100 ft² | 0.6173 yd³ | 0.9259 yd³ | 1.2346 yd³ |
| 120 ft² | 0.7407 yd³ | 1.1111 yd³ | 1.4815 yd³ |
| 200 ft² | 1.2346 yd³ | 1.8519 yd³ | 2.4691 yd³ |
| 500 ft² | 3.0864 yd³ | 4.6296 yd³ | 6.1728 yd³ |
Conversely, one cubic yard covers 324 ÷ depth in inches square feet: 162 ft² at 2 in, 108 ft² at 3 in and 81 ft² at 4 in. Doubling depth doubles volume at the same area.
Turn volume into short tons#
Assume, only for this example, a bulk density of 100 lb/ft³. It is an editable planning value, not a claim that all river rock weighs that amount.
For the 120 ft² bed at 2 in:
120 × 2 ÷ 12 = 20 ft³
20 × 100 = 2,000 lb = 1 US short ton
At 4 in, the same bed contains 40 ft³ and weighs 2 short tons at that density. A separate 10% allowance produces 1.10 and 2.20 short tons respectively. The calculator applies the allowance once to both quantity measures.
Supplier stone size, moisture and void space can change bulk density. The Vulcan aggregate estimator takes a density input independently of dimensions; it is a useful example of the purchasing method, not a river-rock product specification. Ask your supplier for the weight/volume basis of the exact rock. Use the conversion tool if the quote is in tons per yard.
Bags and delivery: keep the selling basis clear#
At 2 in in the example above, 10% allowance gives 2,200 lb. If each hypothetical bag contains 50 lb, buy 44 bags. If the product is sold by bag volume instead, divide the required volume by its labeled yield; do not assume that every 50 lb bag occupies the same volume.
For an arithmetic-only cost scenario, suppose those bags are quoted at $8 each: 44 × $8 = $352 before delivery and tax. A bulk quote of $70 per short ton with $90 delivery instead gives 1.10 × $70 + $90 = $167 before tax. These invented inputs demonstrate comparison math and are not market price estimates. Check minimum orders and delivery access before choosing a supplier.
Decorative coverage and drainage serve different purposes#
A quantity estimate cannot establish drainage performance, slope stability, weed control or a safe walking surface. Confirm the stone grading and the complete installation detail for the intended use. Do not select drainage material from color or coverage alone.
For a different specified ground cover, use the Pea Gravel Calculator. For an angular aggregate or base specification, use the Crushed Stone Calculator. These tools estimate quantities; they do not choose the material for the site.
Before placing the order#
Confirm measured area, chosen depth, product, density basis, bag yield or delivery unit, and any allowance already included by the supplier. Then enter those details in the river-rock tool and save the result with the quote.
Unit references and original worked arithmetic reviewed October 25, 2026. The tables describe hypothetical dimensions and quantities, not an installation specification.