River Rock Calculator
Estimate the volume, weight and cost of river rock for a bed.
Nineteen tabulated rock types, a custom density, and 20 currencies.
Updated October 24, 2026
Introduction
River rock is bought by volume and by weight, while a bed is measured in two dimensions. This calculator joins the three: the length, width and finished depth of a bed become the volume it holds, the wastage you expect becomes the volume to order, and that order becomes a weight at the bulk density of the stone you picked — then a price, from whichever way your supplier quotes.
It is meant for the person placing the order. A homeowner replacing lawn with stone around a patio, a landscaper quoting a dry creek bed and a contractor checking whether a price per ton is better than a price per cubic yard all need the same three numbers, and none of them wants to guess how heavy a cubic metre of the chosen rock is. Nineteen rock types carry typical bulk densities, and a Custom row accepts the figure from a supplier's datasheet.
Every box can also be where you start. Enter a delivery you already have and the depth it will cover comes back; enter a budget and the weight it buys comes back; measure the bed and you get the order to place. The point of the page is to keep those four quantities — area, bed volume, order volume and weight — consistent whichever one you pin down first.
19 rock types
Tabulated from 721 to 2,700 kg/m³, plus Custom
1,425 kg/m³
Standard river rock, the opening density
5%
The opening wastage allowance, editable
How to use the calculator
Six steps, in the order the form reads. The numbers below follow one real walkway through the whole page.
Pick the rock, or keep the stone you have
The Rock type menu loads a typical bulk density for the stone you choose. While a named rock is selected the Density box is locked, because that number belongs to the stone rather than to your project; nothing in the calculation can quietly change it. Choose Custom and the box opens with the current value still in place, ready for a density from the supplier's ticket.
Measure the bed
Length and width describe a rectangular bed, and the area follows. If the surface is already measured — a patio plan, a landscaped area on a drawing — type the area straight into the Area box instead and leave the two sides empty. Mixed units are fine: a length in feet and a width in metres are converted before they are multiplied.
Enter the finished depth of the layer
This is how thick the rock sits once it is spread, not the size of the individual stones. The box opens in centimetres because a decorative layer is usually a few centimetres thick. Settle this before you order: it is the single input that multiplies the whole order, and twice the depth is twice the rock.
Set the wastage allowance
Five percent is the opening figure. The allowance covers what the flat calculation cannot see: loose edges, a rough subgrade, slight over-digging and settling. It is added to the order, not to the bed, so the covered area stays exactly as you measured it. The box needs a positive value, and an allowance above 30% is flagged rather than blocked.
Price it one of two ways
Fill in the price per unit of mass or the price per unit of volume — whichever your supplier quotes — and the other follows through the density. Both money-box menus offer the same twenty currencies, and the total reads in the currency you chose. A quote per cubic yard is not a different price from a quote per ton; it is the same price seen through how heavy the stone is.
Read the volume to order, the weight and the total
A walkway 10 m long and 0.8 m wide, with 7.5 cm of pea gravel and the default 5% allowance:
Covered area
Rock the bed holds
Volume to order
Weight at 1,788 kg/m³
Total at 40 per metric ton
The weight box opens in metric tons, so the page shows 1.12644 there — the same rock as 1,126.44 kg, which is why the weight can look small next to the cubic metres. The price per unit of volume fills itself in at 71.52, the per-metric-ton price seen through 1,788 kg/m³.
The two volume boxes are not the same quantity
Volume is what the bed holds: area times depth. Volume needed is what you buy: the bed volume plus the allowance. When the coverage looks right but the order looks large, the difference is the wastage, not a measuring error — set the allowance to a small positive figure and the two volumes converge.
Because both boxes are inputs, either can drive the other. Type the amount you already have into Volume needed with a known bed and the depth becomes the layer that amount will cover; the allowance is what adjusts when the bed and both volumes are fixed.
How the numbers are worked out
Six statements produce the page, and every one of them runs in both directions, which is why any box can be the one you fill in first.
Bed area: length times width
A 10 m walkway 0.8 m wide covers . Give the area and one side instead, and the other side is worked out.
Bed volume: area times the finished depth
The 8 m² walkway at 7.5 cm holds . Give a total volume with a depth in place, and the area follows.
Volume to order: the bed plus wastage
Here is the allowance as a decimal, so 5% is and the bed volume is multiplied by 1.05.
Weight: the order at the bulk density
The order volume multiplied by the density of the chosen stone. The walkway's 0.63 m³ of pea gravel at 1,788 kg/m³ is 1,126.44 kg, or 1.12644 t.
The two ways a supplier can quote
A price per unit volume is the price per unit mass multiplied by the density. Fill in either price and the other is calculated.
Total cost: weight times the price per unit mass
The total is the weight you are paying for multiplied by the price of that unit of weight.
Cost is one chain, not two
A per-volume quote and a per-mass quote look like separate routes to the total, but they are the same route once a density is chosen, because the two prices are locked together:
That is why entering a quote in either money box gives the same total, and why a rock with a low bulk density can look cheap by the ton and expensive by the cubic yard. The density is the bridge between the two quotes.
Which box moves when you type a total
Typing a derived value makes it the anchor: the calculator then recalculates a neighbour to keep the statements true. Type an area that disagrees with the length and width and one of those sides is recalculated; type a volume with the area in place and the depth gives way; type a budget with a price in place and the weight and order volume follow. The density never moves — it is locked to the menu row, or yours under Custom — which is why a typed weight always resolves through the volume rather than by rewriting what the stone weighs.
After entering a total, glance at the boxes above it. Whichever one changed is the value that was adjusted to make the arithmetic work, and it is usually the one worth checking against your measurements.
Units are converted before they multiply
Each measurement is converted to a common base, then the result is shown in the unit you selected. That is what allows a length in feet, a width in metres and a depth in inches in one calculation. The factors are the definitions of the units rather than rounded approximations:
Two warnings that keep their numbers
A density outside roughly 400 to 3,500 kg/m³ and a wastage above 30% are both accepted, and the field is marked instead. Neither value is impossible, but both are far more often a unit or formatting mistake — a specific gravity such as 1.43 typed into a box that reads kilograms per cubic metre, or a quantity typed into the allowance. The number stays visible, so you can see what the rest of the calculation used while you correct it.
Rock types and bulk density
The density in the second box is a bulk density: it counts the air between the stones, not just the stone itself. That single fact explains most of the surprises in a rock order.
Solid rock is denser than a pile of the same rock, because a pile is part stone and part air. The figures in the menu describe the loose, dry material — the state it arrives in — which is why a cubic metre from one row of the table can weigh nearly four times as much as a cubic metre from another.
The range runs from crushed asphalt at 721 kg/m³ to quartzite at 2,700 kg/m³ — about 3.7 times as heavy for the same cubic metre. That is worth pausing on when comparing suppliers, because the two quotes only become comparable once the density is known: a ton of light rock is a bigger pile than a ton of heavy rock, so a price per ton favours light stone and a price per cubic yard favours heavy stone. A per-ton quote on quartzite buys about a quarter of the volume that the same money buys in crushed asphalt.
Wet stone and compacted stone weigh more
Bulk density moves with the weather and with handling. Wet stone carries water in the gaps between pieces, so the same load weighs more when it arrives in the rain; a layer that has been vibrated or driven over packs tighter, so the same tonnage covers less area. The tabulated figures are a reasonable starting point for a dry, loose delivery.
If your supplier prints a bulk density on the ticket — quarries often do, because the number changes between grades — choose Custom in the Rock type menu and enter it. The weight and every price that depends on it are recalculated from your figure instead.
Weight is the fragile number, volume is the firm one
Depth and area are measurements you can take again; bulk density is an estimate of a pile. Treat the volume to order as the firm part of the answer and the weight as the part to confirm when the load is weighed, especially if you are paying by the ton.
Worked examples
Three situations that start from different knowns: two competing quotes, a pile you already own, and a fixed budget.
Two quotes for the same patio bed
Situation: A 5 m by 4 m bed is to be dressed with 6 cm of standard river rock — 1,425 kg/m³. One supplier quotes 60 per cubic yard; another quotes 45 per metric ton. Which order is cheaper?
Inputs
Result
The page shows 1.26 m³ to order, 1.7955 t, and a total of 98.88 against the cubic-yard quote or 80.80 against the per-ton quote.
In practice: The per-ton quote wins here, but not because tons are cheaper in general: this is a light stone at 1,425 kg/m³, so a ton is a comparatively large volume. On quartzite at 2,700 kg/m³ the same ton is roughly half the rock, and the ranking can flip. Enter both quotes in the two money boxes, one at a time, and compare the totals — the calculator converts each into the same total for you.
A cubic yard you already have
Situation: A neighbour has a spare cubic yard of standard river rock. How deep will it cover a 2 m by 3 m strip at the usual 5% allowance, and what does that pile weigh?
Inputs
Result
The page reads 6 m², 0.728147 m³ of bed volume, a depth of 12.1358 cm and a weight of 1.08949 t.
In practice: Type the delivery into the Volume needed box and the page works backwards: the depth is the layer that amount will cover, and the weight tells you whether you can move it by hand or need the trailer. A cubic yard is a common bulk-delivery unit, so this is also the quick way to check a supplier's stated amount against your bed.
A budget instead of a quantity
Situation: A garden club has 200 to spend on standard river rock at 45 per metric ton, to top up a border at the usual 6 cm. How much stone does the budget buy, and how much bed will it cover?
Inputs
Result
The page reads 4.44444 t, 3.11891 m³ to order and a covered area of 49.5065 m² at a 6 cm layer.
In practice: This is the reverse use that surprises people most: a budget behaves like any other known value, so entering it recalculates the weight and the order volume. Use the resulting area to decide whether the budget covers the whole border, and raise the depth only if the stone size needs it — not to spend the money.
Ordering and measuring tips
The arithmetic is settled by two decisions: how thick the layer should be, and how much extra to order. Everything else follows.
Choose the allowance before you look at the total
The allowance is where you absorb what the flat calculation does not see. For a bed whose measured volume is 2 m³, the common settings differ by a few shovels on a small bed and by a trailer load on a large one:
5%
2.10 m³
Opening figure
10%
2.20 m³
Loose edges
15%
2.30 m³
Rough subgrade
30%
2.60 m³
Flagged, not blocked
Each step adds that share of the bed volume, not of the final order, and the box needs a positive figure — zero is rejected, because an order with no allowance at all is almost always followed by a second trip.
Weigh the order before you plan the trip
The weight box is the payload. One cubic metre of standard river rock is 1.425 t, so the walkway above — 0.63 m³ — is 1.12644 t, and the patio bed at 1.26 m³ is 1.7955 t. A single-axle trailer rated for 750 kg cannot take the patio order in one go, and neither can most car boots; the weight is the number to check against the vehicle, not the volume.
Round up to what the supplier actually sells
Bulk rock is loaded by the scoop, quoted by the cubic yard, the cubic metre or the ton, and often sold with a minimum load. Bags come in fixed volumes. Compare the calculated order with the increments on offer before deciding: a 1.26 m³ order may become 1.5 m³, and that extra is cheaper than a second delivery charge later.
Measure the bed the way the layer will sit
Run the tape along the middle of the bed rather than around the edging. For a bed that tapers, take three widths and use the average, or split it into two rectangles and run each one. For an irregular shape, split it into rectangles and circles and add the volumes — the calculator handles one rectangle at a time.
Keep the layer deeper than the largest stone
The depth you enter is a finished surface, so a layer thinner than the biggest stones will not lie flat however accurate the arithmetic is. For a decorative dressing, a layer comfortably deeper than the largest stone reads as level, and how much deeper depends on the finish you want; a surface that has to bear foot traffic needs more again, and the order grows with it.
Frequently asked questions
Three questions that come up once the numbers start moving.
Is a ton the same as a tonne?
In metric use a tonne is 1,000 kg, and that is the metric ton in the weight and price menus. A US short ton is 2,000 pounds, or 907.18474 kg, and an imperial ton — often called a long ton — is 2,240 pounds, or 1,016.0469088 kg. All three appear in both menus, so a quote in short tons and a quote in long tons differ by about 12% before any price difference is involved:
Ask which ton a quote uses. An identical count of tons buys roughly 109 kg more rock when the ton is imperial, about 12% more material for the same price.
Why is the price per cubic yard so different from the price per ton?
They are the same price seen through the density, not two prices. For standard river rock at 1,425 kg/m³, 45 per metric ton works out to 64.125 per cubic metre, and a cubic metre is 1.30795 cubic yards, so the same price reads 49.0271 per cubic yard.
Because of that link, changing the rock type changes the per-volume price even though the per-ton price has not moved. If you enter a quote per ton, the per-volume box fills in for the stone currently selected — switch rocks and it moves with the density.
Why can't I type in the Density box?
While a named rock is selected, the density is that stone's property rather than an input of yours, so it is locked. That matters because the weight and both prices depend on it: if the box were free, typing a weight or a total would be able to rewrite the density to fit, and the answer would no longer describe the rock you chose.
Choose Custom in the Rock type menu to take control. The current value stays in the box, so nothing in the calculation breaks at the moment of switching, and you can replace it with the figure from a delivery ticket or a supplier's datasheet.
Limitations
This is a planning estimate for placing an order, not a delivered quantity and not a quotation.
- •Bulk density is an estimate of a pile. The tabulated figures describe typical dry, loose stone. Moisture, grading and how the load was handled all move the real number, so confirm the weight your supplier charges for — especially on a per-ton quote.
- •The bed is treated as flat and level. Slope, crowned ground, edging depth and settlement are not modelled, and neither is compaction after spreading. The wastage allowance is your buffer for all of them, so raise it on a site that is not flat.
- •One rectangular bed per calculation. An L-shaped, curved or multi-part area has to be split into rectangles, run in parts, and added up. The area, volume and weight cover only the rectangle currently described.
- •Depth is a finished surface, not a specification. A layer thinner than the largest stone will not lie flat, and a layer that has to bear traffic needs more than a decorative dressing. Nothing here checks stone size against depth.
- •Prices exclude everything but the rock. Delivery, minimum loads, bagging surcharges and taxes are not part of the total, and currency conversion uses a daily rate, so a quote in another currency is indicative rather than binding.
- •It is not a drainage or structural design. River rock around a drain, on a slope or behind a retaining wall has to be sized for water flow and stability, which this page does not model. If you are choosing between this stone and a crushed aggregate for a driveway base, the gravel calculator prices sixteen gravel types the same way.
For a large order, a commercial job or any bed tied into drainage, edging or structural work, treat the volume and weight here as a starting figure and confirm both with the supplier or the designer before the rock is delivered.
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