How to calculate cubic feet for rock
Decorative rock and river stone sell mostly by the ton or cubic yard, but you'll plan jobs in cubic feet to get to a finished depth. Multiply length × width × depth (in feet); for round beds, use π × r² × depth.
Most landscape rock weighs about 105 lbs per cubic foot, or 2,835 lbs per yard.
Worked examples
Example 1: A 30 × 4 ft strip of decorative rock at 3 inches deep
30 × 4 × 0.25 = 30 ft³ = 1.11 yd³ ≈ 1.58 tons.
Example 2: A 12 ft diameter circle of river rock at 2 inches deep
π × 6² × 0.167 ≈ 18.9 ft³ ≈ 0.99 tons.
Example 3: A 60 ft drainage swale, 3 ft wide × 6 inches of rock
60 × 3 × 0.5 = 90 ft³ = 3.33 yd³ ≈ 4.73 tons.
Rock weight reference
| Rock type | Conversion factor | Worked example |
|---|---|---|
| River rock | ~110 lb/ft³ | 1 yd³ ≈ 1.49 tons |
| Decorative gravel | ~105 lb/ft³ | 1 yd³ ≈ 1.42 tons |
| Granite | ~115 lb/ft³ | 1 yd³ ≈ 1.55 tons |
| Limestone (crushed) | ~95 lb/ft³ | 1 yd³ ≈ 1.28 tons |
| Lava rock | ~40 lb/ft³ | 1 yd³ ≈ 0.54 tons |
Tips and considerations
Buy a sample first
Color and stone size vary between deliveries even within the same product. Pick up a small bag and verify against your design before ordering bulk.
Mind the weight
Rock is heavy. A standard pickup truck legally hauls 1 cubic yard of river rock; pretty much anything more requires a delivery truck.
Common mistakes to avoid
- Using one density for all stone. River rock is around 100 lb/ft³, granite landscape rock can hit 165 lb/ft³, lava rock is much lighter at 35–50 lb/ft³. Confirm density before converting cubic feet to tons.
- Forgetting to budget for shape settling. Round river rocks pack with more air gaps than crushed angular stone — the same cubic feet covers more area but holds less material.
- Treating decorative depth like mulch. Decorative rock is typically 2–3 inches deep, not 3–4 inches. Mulch math will overestimate the order.
- Skipping the fabric layer in the cubic feet count. Landscape fabric goes under the rock; the rock depth is measured above it.
Related concepts and calculators
Decorative rock orders pair with these tools:
- Cubic feet to tons — most rock is sold by the ton.
- Gravel — same workflow for crushed stone bases.
- Sand — for the bedding layer beneath river rock or cobbles.
- Cubic feet to square feet — figure out coverage area at a chosen depth.
Frequently asked questions
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