LANDSCAPE ROCK
How much landscape rock do I need?
Measure the net area, choose a depth, multiply, then convert to the unit your supplier sells in. The volume is square feet × depth in inches ÷ 324 cubic yards, or square feet × depth in inches ÷ 12 cubic feet. The measuring and the depth are where orders actually go wrong, so those are the two steps worth slowing down for.
Step 1 — Measure the area you are actually covering
Break the bed into shapes you can measure and add them:
- Rectangle:
length × width - Circle:
π × radius² - Triangle:
base × height ÷ 2
Then subtract what the rock will not cover — the footprint of shrubs and tree trunks, a stepping-stone path through the bed, a bench, an irrigation valve box. A 2 ft diameter shrub removes 3.1416 × 1² = 3.14 sq ft. Four of them is 12.57 sq ft, which on a small bed is a bag you do not need to carry.
Worked: a bed that measures 30 ft × 8 ft with a 4 ft × 4 ft grouping of shrubs left clear is 240 − 16 = 224 sq ft net.
Step 2 — Choose the depth for the job, not a default
Decorative rock depth is a design decision and the same material behaves differently at different depths:
- A thin dressing over soil or over existing gravel reads as a colour change rather than a surface.
- A walking surface needs enough depth that the rock does not scrape through to the membrane underneath.
- A dry creek bed or a drainage swale needs enough depth to hold the flow it is there to carry.
- A border that will be raked or walked on needs more than one only looked at.
This page will not print a depth table, because those depths depend on what is under the rock and what the rock is doing — the same reason the gravel calculator refuses to invent driveway depths. Take the depth from your design or your contractor, and put that number in the formula.
Step 3 — Convert to what you are buying
At 224 sq ft and 2 inches: 224 × 2 ÷ 12 = 37.33 cubic feet, or 224 × 2 ÷ 324 = 1.38 cubic yards.
Now match the unit:
- By the cubic yard: order the yardage, and check what increment the supplier sells — whole yards, half yards, or a minimum load.
- By the bag: divide by the cubic feet printed on the bag and round up. If you only have the bag weight, find the volume — a bag sold by weight tells you nothing about coverage until you have its cubic feet.
- By the ton: ask the supplier for their pounds per cubic yard for that product, or ask them to quote in cubic yards. Rock density varies by type and gradation, and a borrowed figure can change the load count.
The two decisions that move the order more than the math
Waste allowance. Rock is laid by hand around obstacles, and cut and fitted where it meets edging. One supplier's published allowance table runs from 5 percent for a simple layout to 20 percent for complex cuts and patterns. Decide your percentage once, apply it to the total, and do not round per shape.
Weed membrane. It does not change the volume — the rock sits on top of it either way — but it changes how the rock behaves, and it has to be in place before the first load arrives, not after.
Related calculators
The landscape rock calculator covers the volume formula and the supplier-published coverage figures with their sources, and how much does a yard of rock cover answers the reverse question — what a yard you were quoted actually covers. River rock calculator is the same arithmetic for smooth rounded stone, and how much a yard of mulch covers is the same table for a lighter material.
The arithmetic is from the definitions 1 cubic yard = 27 cubic feet and 1 foot = 12 inches. Waste percentages quoted are one supplier's published figures (KRC Rock, Apache Brown product page, read 2026-09-21) and are that supplier's, not a standard.