River Rock Calculator

How to calculate river rock

River rock is sold by the ton or the cubic yard, and both come from the area and depth of your bed.

Cubic yards = length (ft) × width (ft) × depth (in) ÷ 324
Tons = cubic yards × supplier’s tons per yd³ (1.35 is a typical planning value)

The calculator above returns cubic yards, cubic feet, cubic meters, tons, tonnes and 0.5 ft³ bags. Switch to landscape rock for lighter decorative stone (the preset uses 1.3 tons per yd³, a typical planning value; use your supplier’s figure if they give one).

1. Measure the bed. Split curved beds into rectangles, or use average length × average width.
2. Pick the depth from the size of the stone (see below).
3. Add 10% for gaps along edges and uneven ground.
4. Choose bags or bulk. One cubic yard is 54 bags of 0.5 ft³.

How deep should river rock be?

As a rule of thumb, lay river rock at least as deep as the largest stones, so the stones overlap and hide the fabric underneath.

Coverage per ton uses 1.35 tons per yd³. Larger cobbles and boulders do not pack tightly, so for anything bigger than about 5 in ask the supplier how much area a ton covers.

How much rock do I need per 100 ft²?

Because the stone size sets the depth, the size you pick changes the order more than anything else. For every 100 ft² of bed, river rock at 1.35 tons per yd³ takes:

• ¾–1½ in rock at 2 in: 0.62 yd³, about 0.83 tons or 34 bags of 0.5 ft³.
• 1½–3 in rock at 3 in: 0.93 yd³, about 1.25 tons or 50 bags.
• 3–5 in rock at 4 in: 1.23 yd³, about 1.67 tons or 67 bags.
• 3–5 in rock at 5 in: 1.54 yd³, about 2.08 tons or 84 bags.

So the same 300 ft² border needs about 2.5 tons of small rock but 5 tons of large rock at 4 in. Choose the look first, then the depth, then measure; ordering the other way round is how most short or oversized river rock orders happen.

How much river rock for common sizes?

The table covers common beds and borders at 2 in and 3 in deep. Every figure is computed with the site’s calculation library.

How much river rock for a dry creek bed?

Treat a dry creek as a long, narrow rectangle. Use the average width and the depth of stone you will lay, not the depth of the trench. A 3 × 40 ft creek lined 2 in deep needs 0.74 yd³, about 1 ton. Lining it 4 in deep with larger rock doubles that. Boulders along the banks are bought separately, usually by the piece or by the ton, and are not part of this calculation.

If the creek is meant to carry runoff, dig it wider than it looks on paper and slope it gently so water does not undercut the stones. Line the trench with fabric before the rock goes in. For a creek that bends, measure the length along its center line, then multiply by the average width. A meandering 3 ft creek that runs 40 ft through the yard is still about 120 ft² of stone.

For a wider, deeper creek that carries real runoff, the numbers climb quickly. A 4 × 60 ft creek lined 4 in deep with 3–5 in stone is 240 ft², which needs 2.96 yd³, about 4 tons, or 4.4 tons with 10% extra. A narrow 2 × 30 ft rill at 2 in needs only 0.37 yd³, about half a ton, which is 20 bags.

How much river rock for a border around a house?

A border along a wall is a long rectangle: wall length × border width × depth. These figures are at 3 in deep, the usual depth for 1½–3 in stone, at 1.35 tons per yd³.

For a border all the way around a house, do not add the four wall lengths times the width, because that misses the corner squares. Measure the outer rectangle and subtract the house. Around a 40 × 30 ft house, a 2 ft border runs out to 44 × 34 ft: 1,496 − 1,200 = 296 ft². At 3 in that is 2.74 yd³, about 3.7 tons, or 4.07 tons with 10% extra. A 3 ft border on the same house is 456 ft², 5.7 tons, or 6.27 tons ordered. Leave out door steps, the driveway and any section you plan to plant.

How much river rock around a tree?

A tree ring is a circle minus the trunk. Work out 3.1416 × radius² for the ring’s outer edge and subtract the trunk area. With a 1 ft trunk:

Bags are 0.5 ft³, before the 10% extra. Small rings like these are usually a bag job: four 6 ft rings at 2 in take about 37 bags, or 41 with 10% extra. Keep the stone back from the trunk itself and do not pile it up against the bark, which traps moisture.

Beds with plants: subtract the openings

In a planted bed, the shrubs and perennials take up space you do not cover. Count the plants, estimate the bare circle you will leave around each, and subtract. A 10 × 20 ft bed with eight plants, each with a 2 ft opening, loses 8 × 3.14 = 25.1 ft², leaving 174.9 ft². At 3 in deep that is 1.62 yd³, about 2.19 tons or 88 bags, against 2.5 tons and 100 bags for the bare bed. On beds with many plants the saving is worth the five minutes of counting.

River rock for downspouts and drip lines

Splash pads under downspouts are small but deeper than a decorative bed, often 4 in, so water does not scour the soil. A 2 × 4 ft splash area at 4 in deep takes 2.7 ft³, about 0.13 tons or 6 bags of 0.5 ft³. Four downspouts take 0.53 tons, or 22 bags (24 with 10% extra). For a gravel drip line along the eaves, use the border table above with the width of the strip you dig. If the water needs to be carried away rather than just spread, size a French drain trench with the gravel calculator instead.

River rock or landscape rock?

The calculator offers both. River rock is rounded, water-worn stone. The calculator uses planning values of 1.35 tons per yd³ for river rock and 1.3 for the landscape rock preset. These are typical estimates, not published figures, so use your supplier’s weight per yard when you have it. The volume for a bed is the same; only the tonnage changes.

For a 20 × 10 ft bed at 3 in, both need 1.85 yd³, which is 2.5 tons of river rock or 2.41 tons of landscape rock. Some decorative stone weighs much less than either preset, so for those products ask the supplier for its weight per yard and use it, or order by the yard. For 3–5 in river rock laid 5 in deep, a 10 × 10 ft bed needs 1.54 yd³, about 2.08 tons, and a 3 × 50 ft border 2.31 yd³, about 3.13 tons.

How much does river rock weigh?

A cubic yard of river rock weighs about 1.35 tons, or 2,700 lb, roughly 100 lb per cubic foot. A 0.5 ft³ bag therefore holds about 50 lb. That is a planning value, not a measured one, and wet stone weighs more, so if your supplier quotes a weight per yard, multiply the cubic yards by their figure.

River rock per square metre

In metric, the 1.35 US tons per yd³ planning value is about 1.6 tonnes per m³; use your supplier’s figure if they give one.

Multiply length × width in metres by depth in metres for m³, then by 1.6 for tonnes. A 5 m border 1 m wide at 50 mm is 0.25 m³, about 0.4 tonnes, or 0.44 tonnes with 10% extra. A 4 × 3 m bed at 50 mm is 0.6 m³, about 0.96 tonnes, and a 10 m dry creek 1 m wide lined 75 mm deep is 0.75 m³, about 1.2 tonnes. At 40 mm, for small 20–40 mm cobbles, one tonne covers about 15.6 m².

How many bags of river rock, by bag size?

Bags are sold by volume or by weight, and sizes differ between stores. Use the volume on the label and this table, or divide your total pounds by the bag weight.

To check a bulk delivery against your plan, remember that one ton of river rock is about 20 ft³. The 2.06 tons for the 3 × 50 ft border above is about 41 ft³; if your wheelbarrow carries about 3 ft³ a trip (check its rated capacity; rock is heavy, so weight is often the limit), that is 14 trips. Have the load tipped as close to the bed as the truck can safely reach, on a tarp if it lands on lawn.

Common mistakes when ordering river rock

River rock is bought once and rarely topped up, so a short or oversized order is costly to fix. Watch for these:

• Choosing the depth before the stone size. A 3 × 50 ft border of 1½–3 in rock needs 3 in, 1.88 tons. Ordering for 2 in brings 1.25 tons, about 0.63 tons short, and the fabric shows through.
• Ordering tons when you worked out yards. At 1.35 tons per yd³, treating the yard figure as tons leaves you about 26% short.
• Using trench depth for a dry creek. Calculate the depth of stone you lay, not the depth you dig. A 3 × 50 ft creek lined 4 in deep needs 1.85 yd³ (2.5 tons); entering a 12 in trench would triple that.
• Counting bags for large beds. A 500 ft² bed at 3 in is 250 bags of 0.5 ft³, about 6.25 tons to lift by hand. Price bulk delivery first.
• Including boulders in the tonnage. Accent boulders are sold by the piece or ton and do not pack like river rock, so add them separately.
• Adding wall lengths for a full house border. Around a 40 × 30 ft house, 140 ft of wall × 2 ft = 280 ft², but the real 2 ft border is 296 ft² because of the four corner squares. Measure the outer rectangle and subtract the house.

River rock calculator vs gravel, pea gravel and mulch calculators: which one to use

Use this calculator for decorative beds, borders and dry creeks in rounded stone, where the stone size sets the depth. For neighbouring jobs:

• Pea gravel calculator: small round stone for patios, paths and dog runs you walk on.
• Gravel calculator: compacted crushed stone for shed bases, slab bases and French drains.
• Mulch calculator and topsoil calculator: the planted parts of the same bed.
• Tons to cubic yards: comparing a per-ton quote with a per-yard one.

Tips before you order

• Lay landscape fabric first and pin it. River rock does not stop weeds by itself.
• Edge the bed so stones stay out of the lawn and mower.
• Check the size grading. “River rock” is sold in many size ranges; the size sets the depth and the coverage.
• Get a sample or photo of the color in daylight, since wet and dry stone look different.
• Compare bags and bulk by converting both to the same unit with the tons to cubic yards converter. Delivery fees and minimum loads vary, so ask local yards.

The same measurements size the rest of the shopping list. Landscape fabric covers the bed area plus overlap at the seams, so a 3 × 50 ft border needs at least 150 ft² of fabric. Edging runs along every side that meets lawn: for that border against a house wall, that is the 50 ft front edge plus the two 3 ft ends, 56 ft in all. Buy the fabric, pins and edging in the same trip, because they go down before the first load of rock.