Free River Rock Calculator calculator
Enter the area to cover and the depth, and this river rock calculator returns the cubic yards, cubic feet, weight in pounds and tons, and the number of 50-lb bags to buy — updated live, as you type.
On this page11 sections
Estimates only. Density of 95 lb/ft³ is a typical figure — confirm with your supplier for exact rock type.
Results are estimates. Consult a professional.
How the river rock calculator works
The calculator converts a coverage area and a target depth into volume, then multiplies by the density of river rock to get weight. Volume comes first: multiply the square footage by the depth in inches, then divide by 12 to express it in cubic feet. Divide by 27 for cubic yards. Weight comes from multiplying volume by the density of river rock — about 95 pounds per cubic foot — and the bag count rounds up so you never run short.
How deep to lay river rock
Depth is the single biggest driver of how much rock you need — going from 2 inches to 4 inches doubles the volume. The right depth depends on the application: decorative groundcover around plants needs less rock than a drainage swale or dry creek bed. Using too little rock leaves gaps where weeds push through; using too much smothers plant roots and wastes money.
| Application | Recommended depth | Notes |
|---|---|---|
| Decorative ground cover | 2 in | Suppresses weeds, stays tidy |
| Pathway or walkway | 2–3 in | Thick enough to walk on comfortably |
| Foundation drainage | 3–4 in | Directs water away from the house |
| French drain backfill | Full trench depth | Surrounds the perforated pipe |
| Dry creek bed | 4–6 in | Mimics a natural streambed |
| Erosion control on slopes | 4–6 in | Heavier material stays in place |
Depths are center-of-installation values. Layer thickness directly over landscape fabric can be reduced by 20–25% because the fabric prevents rock from sinking into the soil.
River rock density and weight
River rock weighs roughly 95 pounds per cubic foot, or about 1.28 tons per cubic yard. This is denser than mulch (15–20 lb/ft³) but lighter than gravel aggregate (100–110 lb/ft³) because river rock is rounded and washed — there are more air gaps between stones. The density matters when you are loading a pickup truck or calculating a delivery cost per ton.
Pickup truck capacity
A half-ton pickup safely carries 1,000 to 1,200 pounds of payload — about 10 to 13 cubic feet of river rock, or roughly 0.4 cubic yards. A full-size three-quarter-ton pickup can handle up to 1,800 pounds — about 19 cubic feet, or 0.7 cubic yards. For jobs over 1 cubic yard, a bulk delivery is faster and often cheaper.
River rock for drainage vs landscaping
River rock is used for two very different purposes in a yard, and the right stone size changes between them. For landscaping — decorative mulch around plants, pathways, and borders — small to medium stones (¾ inch to 2 inches) look the best and stay in place. For drainage — French drains, drywell backfill, downspout extensions, and swales — larger stones (1.5 inch to 4 inch) allow faster water movement between the voids.
| Purpose | Best stone size | Why |
|---|---|---|
| Decorative / mulch | ¾ in – 1½ in | Tidy appearance, easy to rake |
| Pathway | ¾ in – 1½ in | Comfortable underfoot |
| French drain | 1½ in – 3 in | High void space for drainage |
| Dry creek bed | 2 in – 6 in | Natural, cobble-like look |
| Erosion control | 3 in – 6 in | Heavy enough to resist water movement |
Stone size affects void volume, which in turn affects how much water moves through the layer per hour. Drainage applications should not use very small pea gravel, which packs tightly and slows water movement.
Worked example: a 10 × 20 ft landscape bed at 2 inches deep
Priya is replacing the mulch around her front foundation planting with small river rock. The bed is 10 ft wide and 20 ft long, and she wants a 2-inch depth for a clean, weed-suppressing layer.
Step 1 — Calculate volume
Area = 10 × 20 = 200 ft². Volume = 200 × 2 ÷ 12 = 33.3 cu ft. In cubic yards: 33.3 ÷ 27 = 1.23 cu yd.
Step 2 — Calculate weight
Pounds = 33.3 × 95 = 3,163 lb. Tons = 3,163 ÷ 2,000 = 1.58 tons.
Step 3 — Count bags or order bulk
In 50-lb bags: ⌈3,163 ÷ 50⌉ = 64 bags. At ~$5–6 per bag, that is $320–$384 worth of bagged rock. A 1.5-ton bulk delivery typically costs $150–$250 including delivery, making bulk the better value for jobs this size.
Installing river rock: step-by-step
Lay landscape fabric first — it is the most important step for any river rock installation. Without it, rock sinks into the soil within a season and weeds push up through the gaps. Use woven polypropylene fabric (not plastic sheeting, which blocks water), overlap seams by 6 inches, and secure the edges with staples before spreading the rock.
- Clear the area of weeds, debris, and old mulch.
- Grade the soil so water drains away from the house or structure.
- Lay woven landscape fabric over the entire area, overlapping seams 6 inches.
- Cut X-shaped slits in the fabric for any plants to grow through.
- Spread the river rock evenly with a rake, starting from one corner.
- Tuck the fabric edges under edging or borders to keep it in place.
- Top up with more rock after the first season as it settles.
River rock vs mulch: which to choose?
River rock and mulch both suppress weeds and retain moisture, but they have very different long-term maintenance profiles. Rock does not decompose, so it lasts indefinitely and needs no annual replacement — but it absorbs heat in summer (which can stress nearby plants), does not improve soil, and is very difficult to remove once laid. Mulch decomposes over 1–3 years into organic matter that feeds the soil, stays cool under plant roots, and is easy to remove or top up — but it needs replacing annually.
| Factor | River rock | Organic mulch |
|---|---|---|
| Longevity | Permanent | 1–3 years |
| Weed suppression | Good (with fabric) | Good |
| Summer heat | Gets hot | Stays cool |
| Soil improvement | None | Yes (as it decomposes) |
| Drainage | Excellent | Good |
| Annual cost | Zero (after install) | Yearly top-up |
River rock is the better choice near driveways, foundations, and fire-prone areas where organic material is a hazard. Mulch is better under trees and shrubs where soil improvement matters.
Frequently asked questions about the free River Rock Calculator calculator
About this river rock calculator
This river rock calculator runs entirely in your browser. Nothing you enter is sent anywhere — the cubic yards, weight, and bag count update instantly as you adjust the area or depth. It uses 95 lb/ft³ as the standard density for clean river rock, which matches most bagged-product labels and bulk landscape supply data.
It is part of our free home & garden calculators. For other ground-cover materials, see the mulch calculator, the topsoil calculator, or the full calculator library.