How this calculator works for landscape gravel
Decorative gravel — the kind you see in xeriscape beds, around shrubs, or as a mulch alternative — is sized by area × depth, with depth as the variable that changes everything. Most landscape projects look best at 2–3 inches:
- 2 inches — minimum to hide weed barrier fabric. Smaller stones (3/8" pea gravel, decomposed granite) work fine here.
- 3 inches — the sweet spot for larger decorative stones (river rock 1"-3", lava rock). Looks finished, suppresses weeds, doesn't waste material.
- Don't go above 4 inches. Any deeper and you are buying material that does nothing — the visible surface is the same.
Match the stone size to the bed size
Big beds (200+ sq ft) handle 2"-3" river rock without looking chunky. Small beds (under 50 sq ft) and beds along narrow paths look better with 3/8" pea gravel or decomposed granite — proportional matters.
Recommended depth & material
| Use | Depth | Material | Notes |
|---|---|---|---|
| Decorative bed (around shrubs) | 2" – 3" | River rock, decomposed granite, lava rock | Over weed barrier and edged. |
| Garden path | 2" – 3" | Pea gravel or decomposed granite | Compacted base under preferred. |
| Dry creek bed | 4" – 6" | Mixed river rock 1"-6" | Larger stones at the edges, smaller mid-stream. |
| Xeriscape ground cover | 2" – 3" | Lava rock or crushed granite | Lava rock weighs half as much per yard. |
| Around foundation (drip-line) | 3" – 4" | River rock or #57 | Slope away from house; helps drainage. |
| Tree well / mulch ring | 2" – 3" | River rock | Keep a 2" ring away from the trunk. |
How to measure landscape beds
Landscape beds are rarely rectangles — they curve, taper, and have cutouts for plants. The calculator's multi-area mode is built for this.
- Sketch the bed shape. Walk the perimeter with chalk or a marker paint. Curves are easier to break into rectangles than to measure as curves.
- Decompose into rectangles. Most kidney-shaped or freeform beds become 2–4 overlapping rectangles plus a half-circle on the end. Measure each piece in feet.
- Add each rectangle to multi-area. Open multi-area mode in the calculator. Add a row per rectangle (label them so you can keep track).
- Don't subtract for plants. Plants take up trivial bed volume — under 5%. The 10% buffer absorbs it. Saves a tedious calculation.
- Pick depth and material. 3 inches of river rock is the default. Switch to 2 inches if you're using fine pea gravel or decomposed granite.
- Add 15% buffer for irregular shapes. Curves, slopes, and gaps around plants always cost more material than the math suggests. Bump from 10% to 15% on freeform beds.
Worked example: 200 sq ft front-yard bed, 3" river rock
A typical decorative bed wrapping a front porch: 200 sq ft total at 3 inches of river rock.
- Volume: 200 × 3 ÷ 324 = 1.85 yd³
- Weight: 1.85 × 2,550 ÷ 2,000 = 2.36 tons
- With 15% buffer (irregular shape): ~2.13 yd³ / ~2.7 tons of river rock.
- Cost: river rock typically runs $65–$85/ton delivered. At $75/ton, that's ~$200 in stone plus delivery.
- Add weed barrier: 200 sq ft of woven geotextile (~$60) and edging (~$80–$120 depending on material).
Total project: $350–$420 for materials. Compare to mulch at the same volume: cheaper up front (~$100) but reapplied every year. River rock is a one-time investment.