Rock Calculator

What the rock calculator tells you

The calculator gives an estimate of the rock or gravel quantity for a project. It uses the project area and the material depth.

Cubic yards measure volume. Tons measure weight. The calculator shows the two quantities, plus the number of bags to buy.

Project examples include driveways, paths, drainage layers, decorative landscape beds, and French drains. A French drain is a gravel-filled trench with a pipe that carries water away.

The quantity estimate does not specify drainage performance or the correct material for a structural base.

How rock quantity is calculated

Use the same unit for length, width, and depth.

1. Measure the length in feet.
2. Measure the width in feet.
3. Divide the depth in inches by 12.
4. Multiply the length by the width.
5. Multiply that result by the depth in feet.
6. Divide the volume in cubic feet by 27.

Formula

$$\text{Volume (cu ft)}=\text{Length (ft)}\times\text{Width (ft)}\times\text{Depth (ft)}$$ $$\text{Volume (cu yd)}=\frac{\text{Volume (cu ft)}}{27}$$

For example, an area of 20 feet by 10 feet has a rock layer 3 inches deep. The base volume is approximately 1.85 cubic yards.

Rock calculator in tons

Bulk density is the weight of loose material per unit of volume. It includes the spaces between stones.

$$\text{Weight (US tons)}=\text{Volume (cu yd)}\times\text{Bulk density (US tons/cu yd)}$$

Example densities of approximately 1.3-1.5 US tons per cubic yard can apply to some landscape aggregates. Stone size, moisture, and compaction can change the density.

The calculator starts with 1.4 US tons per cubic yard for crushed stone. This is an example, not a fixed material property.

At that density, 1.85 cubic yards weighs approximately 2.59 US tons before additional material. A US short ton is 2,000 pounds.

A metric tonne is 1,000 kilograms. The two units are not equal.

Pea gravel calculator: typical project depths

Pea gravel consists of small, rounded stones. The calculator uses an example density of 1.35 US tons per cubic yard.

The table gives initial depth estimates, not construction specifications.

Soil, stone size, drainage, and expected load can change the necessary depth. A deeper layer can be necessary for larger decorative stones.

The landscape rock guide relates coverage depth to stone size.

Rounded pea gravel is not equivalent to graded crushed stone for a structural base. The depth table does not make materials interchangeable.

1. Examine the project's material specification.
2. Use the specified finished depth.
3. Contact the supplier for the loose quantity necessary to obtain the finished volume after compaction.

River rock calculator: ordering tips

River rock is rounded stone that suppliers sell in different sizes. The calculator uses an example density of 1.5 US tons per cubic yard.

A 5-10% additional allowance can compensate for small material losses or settling. Compaction can make a different allowance necessary.

1. Add a different area for each project section.
2. Enter the supplier's bulk density.
3. Enter the supplier's additional-material allowance.
4. Find the supplier's sales unit: cubic yard, US ton, or metric tonne.
5. Find the supplier's minimum order and available increments.

Do not count overlapping areas two times. The quantity to order includes the entered additional percentage.

Use the supplier's density and material specification, not the example values.

Rock calculator: compare bulk material and bags

Bulk cost equals the quantity to order multiplied by the price per unit, plus the entered delivery fee.

The bag count rounds up to full bags. Bags can specify weight in pounds or volume in cubic feet.

1. Select the unit that matches the bag label.
2. Enter the quantity in each bag.
3. Enter the bag price.
4. Compare the bag cost with the bulk quote.

The bag cost does not include delivery. The two estimates do not include tax or installation labor.

Related tools and sources

• Use the cubic yard calculator for a volume estimate without rock weight.
• Use the cubic feet calculator for box-shaped volumes in cubic feet.
• Use the concrete calculator for concrete above a gravel base.
• Use the Pythagorean theorem calculator for right-triangle side lengths in project areas.
• Use the percentage decrease calculator to compare a reduced supplier price with the initial price.

NIST conversion factors give the standard unit conversions.