Rock Calculator
Decorative rock yards and tons by area and depth
What is rock calculator?
A rock calculator answers the homeowner’s first question on any decorative-rock or xeriscaping project: how many tons or cubic yards do I need delivered. The volume math is straightforward — area times depth — but landscape supply yards sell rock by the ton, and the conversion depends on rock type.
The default density is 95 lb/ft³, which is typical for general-purpose 1-2 inch decorative rock. Heavier basalt and granite run 100-110 lb/ft³ and weigh 10-15% more per yard. Lava rock and pumice are much lighter — 50-70 lb/ft³ — so always tell your supplier what you’re ordering and confirm tonnage on the quote.
Picking a size: 1-2 inch rock is the all-purpose default for ground cover and beds — large enough to stay where you put it, small enough to walk on barefoot if you must. 3-4 inch rock is better for steep slopes (less rolling) and dry creek bed centers. Anything finer than half-inch tracks into soil and migrates indoors on shoes; save pea gravel for paths where it’s contained.
Bulk vs bagged: rock at the home center comes in 0.5 or 0.75 cu ft bags at $5-10 each — fine for a 4 ft x 4 ft bed but absurdly expensive past that. Bulk decorative rock at landscape supply yards runs $50-100 per ton delivered (much higher than gravel because it’s sized, washed, and often quarried from premium sources). By the time you’re past about 1 cubic yard, bulk wins on price and saves dozens of trips to the truck.
The 10% waste factor default covers spread loss and edge slip. For dry creek beds and other narrow features where rock ends up outside the intended zone, bump to 15%. Always lay heavy non-woven landscape fabric beneath decorative rock — without fabric, it slowly sinks into soil over 3-5 years and you end up topping off year after year.
When to use a rock calculator
- Xeriscape ground cover — Replace turf with 2-3 inches of decorative rock around drought-tolerant plantings. Output in tons matches supplier pricing.
- Dry creek bed — Mixed 1-3 inch rock over fabric for a drainage feature. Width varies along the run; use average width for the volume estimate.
- Around-the-foundation rock band — 2 inches of 1-2 inch rock as a maintenance-free border. The bag count and tonnage outputs make the bulk-vs-bagged call easy.
How to use the Rock Calculator
- Measure the area — For rectangular beds, length times width. For irregular xeriscape areas, break into rectangles and add. For dry creek beds, use average width times length.
- Pick a depth — Use 2 inches over landscape fabric for ground cover, 3 inches if you skip the fabric (rocks sink slowly into bare soil). 6 inches for a dry creek bed feature.
- Read the tonnage — Decorative rock is sold by the ton at most landscape supply yards. Output shows tons (1 cu yd weighs about 1.28 tons at the default density).
- Apply waste factor — 10% covers spread loss and uneven distribution. Bump to 15% if your area has a lot of edge perimeter relative to interior.
Worked examples
30 ft x 20 ft xeriscape at 3 in
Input: 30 ft x 20 ft x 3 in depth
Output: 5.55 cu yd / 7.13 tons (with 10% waste)Dry creek bed, avg 4 ft x 40 ft x 6 in
Input: 4 ft x 40 ft x 6 in depth
Output: 2.96 cu yd / 3.80 tonsLay landscape fabric beneath to keep the rock from sinking into soil over time.
Foundation border, 2 ft x 80 ft at 2 in
Input: 2 ft x 80 ft x 2 in depth
Output: 0.99 cu yd / 1.27 tons