Solid rock density derived from WSDOT's own riprap equivalences
You calculate gravel in cubic yards and the supplier sells it by the ton, and every gravel calculator bridges the two with a density it got from nowhere. Solid rock can be pinned down: WSDOT sizes riprap by weight and volume together, and both equivalences give about 149 lb per cubic foot. Your pile is not solid rock. It is that, less however much of it is air, and nobody publishes that figure for the heap in your driveway.
Gravel volume, and tonnage if you have a density
ft
ft
ft
in
%
%
lb/cu ft
Tonnage is only calculated if you supply a density. Ask your supplier: they weigh the material every day and it is the one figure somebody actually knows.
Specification summary
Generated from on .
Reopen that address to reproduce these figures exactly.
Entered
Result
One cubic yard of rock, and one cubic yard of pile
Worked example
A 40 ft by 12 ft driveway base at a finished 4 in, compacted, with a 20% compaction allowance and 5% waste. No density entered.
Area. 40 × 12 = 480 sq ft.
Finished volume. 480 × 4/12 = 160 cu ft = 5.93 cu yd.
Loose to order. The compactor takes 20% out, so you have to deliver 7.11 cu yd to end up with 5.93.
With waste.7.47 cu yd.
Tonnage. Not calculated, because no density was entered.
The anchor. Solid rock is about 149 lb per cubic foot, so 2.01 tons per solid cubic yard.
Two things worth taking away. The compaction allowance alone is 1.18 cubic yards on a small driveway, about 20%, and it is the difference between finishing the job and driving back to the yard. And the tonnage is blank on purpose: at a third voids that 7.47 cubic yards is about 10.5 tons, at a quarter voids it is 11.3, and the difference is most of a delivery ticket. Your supplier weighs the stuff daily. Ask them.
The formula
Volume is easy. The two multipliers after it are the argument:
V = A × d/12 order = V(1 + c)(1 + k) tons = order × ρ / 2000
A, d
area in sq ft and FINISHED depth in in, after compaction
c
compaction allowance. Ours, defaulting to 0.20, zero if nothing is compacted
k
waste allowance
ρ
density in lb per cu ft. Yours, from your supplier, not from this page
149
solid rock, derived from WSDOT. Your material is that less its voids
The last term is the only one this page refuses to fill in. Everything to the left of it is geometry and a stated allowance; everything that depends on rho is a property of a specific pile of stone in a specific yard on a specific day.
Why the tonnage is blank
Every gravel calculator on the internet converts cubic yards to tons. None of them cite anything, and after a long look for a source, the reason is clear: there is not one.
State DOT specifications, which is where aggregate is described most rigorously, set what a product must achieve. Gradation, degradation factor, Los Angeles wear, specific gravity. They do not tabulate what a heap of it weighs, because that is not a property of the product, it is a property of the heap.
What can be sourced is the rock. WSDOT sizes riprap by naming a weight and a volume for the same stone, twice, and both come out at about 149 lb per cubic foot. That is solid stone with no air in it, and it is a genuine anchor: whatever your material weighs, it weighs less than that.
How much less is the void fraction, and it moves with gradation, moisture and how the pile was tipped. A third is a common working figure and it is still a guess. So this page gives you the volume, shows you the solid-rock anchor and the arithmetic, and leaves the density to the person who weighs it: your supplier.
One rock, different void fractions
Void fraction
Density
Per cubic yard
Tons per cubic yard
0%
149 lb/cu ft
4,025 lb/cu yd
2.01 tons/cu yd
solid rock, no voids
20%
119 lb/cu ft
3,220 lb/cu yd
1.61 tons/cu yd
25%
112 lb/cu ft
3,019 lb/cu yd
1.51 tons/cu yd
30%
104 lb/cu ft
2,818 lb/cu yd
1.41 tons/cu yd
typical range for a loose graded aggregate
35%
97 lb/cu ft
2,616 lb/cu yd
1.31 tons/cu yd
typical range for a loose graded aggregate
40%
89 lb/cu ft
2,415 lb/cu yd
1.21 tons/cu yd
typical range for a loose graded aggregate
45%
82 lb/cu ft
2,214 lb/cu yd
1.11 tons/cu yd
Read 2026-09-08. The solid figure is derived from WSDOT's own riprap weight and volume equivalences. Every row below it is that figure less a void fraction, and the void fraction is the part nobody publishes.
What a cubic yard weighs, and why nobody can tell you
The rock itself can be pinned down. WSDOT sizes riprap by giving weight and volume together for the same stone:
Heavy loose riprap shall meet the following requirements for grading: Minimum Size, Maximum Size. 30% to 90%: 1 ton (1/2 cu. yd.). 60% to 90%: 300 lbs. (2 cu. ft.) to 1 ton (1/2 cu. yd.). 10% to 30%: 3 inch, 50 lbs. (spalls).
Run both equivalences. 2,000 lb in half a cubic yard is 148 lb per cubic foot. 300 lb in 2 cubic feet is 150. They agree, and they agree because they are both describing solid rock: about 149 lb per cubic foot, or 4,025 lb, near enough two tons, per solid cubic yard.
Your pile is not solid rock. Between the stones is air, and how much depends on the gradation: uniform stone has more voids than a well-graded mix that packs its own fines into the gaps. Wet material weighs more than dry. A freshly tipped pile is looser than one that has sat in the rain.
What the same rock weighs at different void fractions
Void fraction
Density
Per cubic yard
Tons per cubic yard
0%
149 lb/cu ft
4,025 lb/cu yd
2.01 tons/cu yd
solid rock, no voids
20%
119 lb/cu ft
3,220 lb/cu yd
1.61 tons/cu yd
25%
112 lb/cu ft
3,019 lb/cu yd
1.51 tons/cu yd
30%
104 lb/cu ft
2,818 lb/cu yd
1.41 tons/cu yd
typical range for a loose graded aggregate
35%
97 lb/cu ft
2,616 lb/cu yd
1.31 tons/cu yd
typical range for a loose graded aggregate
40%
89 lb/cu ft
2,415 lb/cu yd
1.21 tons/cu yd
typical range for a loose graded aggregate
45%
82 lb/cu ft
2,214 lb/cu yd
1.11 tons/cu yd
The 2,700 lb per cubic yard that every gravel calculator quotes sits at about a third voids, which is a reasonable guess and is still a guess. This page will not print it as an answer. Ask your supplier what their material weighs, because they weigh it every day on the way out of the yard, and it is the one number in this whole calculation that somebody actually knows.
Order the loose volume, not the finished one
The depth you want is the depth after the plate compactor has been over it. That is not the depth that arrives on the lorry.
Base course compacts, and a 4 in finished layer needs meaningfully more than 4 in of loose material spread to get there. The default here is 20%, it is ours rather than a standard, and it is an input because the real figure depends on the material and how hard it is worked.
Getting this wrong is the classic small-job failure. The yardage looks right on paper, the delivery is spread, the compactor goes over it, and the finished level is short of the string line with the driver already gone.
It does not apply to everything. Decorative stone is spread and left, so set the allowance to zero. Drainage rock in a trench is not compacted either, and should not be. A driveway base under pavers is compacted hard and the allowance is real.
Depth, and the layer nobody counts twice
A paver or slab installation usually has two aggregate layers with different depths, and it is easy to price one and lay two.
The base is the structural layer, compacted, and it is the deep one. The bedding layer on top of it is thin, uncompacted before the pavers go down, and it is a different material with a different gradation. They arrive separately and they are ordered separately.
Run this page twice, once for each, rather than adding the depths together, because the compaction allowance applies to one and not the other.
What a landscape yard actually sells you
Yards sell by the ton, by the cubic yard, or by the scoop, and the three are not interchangeable without exactly the density this page will not print.
Ask two questions when you ring. What does a cubic yard of this material weigh, and are you selling by weight or volume? The first has a real answer because they weigh loads across a scale all day. The second decides whether the number you calculated is the number you order.
The scoop is the one to pin down. A yard's scoop is whatever their loader bucket holds, it is often not a cubic yard, and it varies between yards. It is a unit of convenience rather than measurement.
Compaction, and the depth that arrives against the depth you keep
The second thing missing from a gravel order is that base course is delivered loose and compacted in place.
Four inches of compacted base did not arrive as four inches of material. It arrived as noticeably more, and the plate compactor took the difference out. Order the finished volume and you are short by exactly the amount the compaction removed, which is the point at which somebody drives back to the yard.
How much depends on the material and the effort, and it is not a figure this page will publish either, for the same reason as the density. It is an input, it defaults to a round 20%, and it is labelled as ours rather than dressed up as a standard.
It does not apply to everything. Decorative stone spread and left alone is not compacted, so the allowance should go to zero. A driveway base under pavers is compacted hard and the allowance is real. Drainage rock in a trench is somewhere between, and it is not compacted at all if it is doing its job.
The source, and what it does not cover
Read 2026-09-08. 2027 Standard Specifications M 41-10, Division 9 Materials, Washington State Department of Transportation, section 9-13.1(2). Sizes riprap by weight and volume together, which is the only place found that pins a stone's weight to its volume in a government publication. Both equivalences give about 149 lb per cubic foot, which is SOLID rock rather than a loose pile.
That document sets minimum properties for engineered aggregates: gradation, degradation factor, Los Angeles wear, specific gravity. What it does not contain, and what no government publication found from here contains, is a table of typical loose densities for the materials sold at a landscape yard. The specifications describe what a product must achieve, not what a heap of it weighs.
Which is the honest answer to why every gravel calculator's tonnage figure is uncited. There is nothing to cite.
Frequently asked questions
How many cubic yards of gravel do I need?
Area in square feet times the finished depth in inches, divided by twelve to get cubic feet, then by 27. A 40 by 12 ft driveway at 4 in is 5.93 cubic yards finished. Add a compaction allowance on top of that if the material is being compacted, because the loose volume delivered has to be larger than the finished volume.
How much does a cubic yard of gravel weigh?
It depends on the material and nobody publishes it for yours. Solid rock is about 149 lb per cubic foot, or 4,025 lb per cubic yard, derived from WSDOT's own riprap weight and volume equivalences. A loose pile is that less its void fraction, which is commonly around a third, giving roughly 2,700 lb. That is a guess at the voids, not a measurement of your material.
How do I convert cubic yards of gravel to tons?
Multiply by the density and divide by 2,000, and the density has to come from your supplier. They weigh loads over a scale daily, so they have a real number. A calculator that converts without asking has assumed a void fraction on your behalf, and between a quarter and a third of voids is over a ton of difference on a ten-yard order.
How much extra gravel for compaction?
This page defaults to 20% and labels it as its own figure rather than a standard. The real amount depends on the material and the compaction effort. It applies to base course under pavers or a driveway, and not at all to decorative stone that is spread and left or to drainage rock in a trench.
How deep should a gravel driveway base be?
That is a design question this page does not answer, because it depends on the soil beneath, the drainage and what is going to drive on it. The calculator takes whatever finished depth you specify and works out the loose volume needed to achieve it.
What is a scoop of gravel?
Whatever that yard's loader bucket holds, which is often not a cubic yard and varies between yards. It is a unit of convenience rather than measurement. If you are buying by the scoop, ask what a scoop is in cubic yards before comparing prices.
Why do gravel calculators disagree with each other?
Because they use different assumed densities and none of them say so. The volume arithmetic is identical everywhere and cannot disagree; the tonnage depends entirely on an unpublished void fraction, so two calculators can differ by 20% on the same job and both look authoritative.
Check these numbers yourself
2027 Standard Specifications M 41-10, Division 9 MaterialsWashington State Department of Transportation, section 9-13.1(2). Sizes riprap by weight and volume together, which is the only place found that pins a stone's weight to its volume in a government publication. Both equivalences give about 149 lb per cubic foot, which is SOLID rock rather than a loose pile.
How every figure here is verified: Sources & Method. Who builds this: About. Found something wrong? Tell us and it gets fixed or removed.
Figures on this page last checked against the source documents on 2026-09-08. Codes are amended locally; confirm against the edition your jurisdiction enforces.
The tonnage is deliberately blank until you supply a density. No government publication found from here tabulates loose densities for landscape aggregates, because that is a property of a specific pile rather than of a product. The solid-rock anchor is derived from WSDOT's riprap equivalences, read 8 September 2026. Compaction and waste allowances are this page's own figures and are inputs. Base depth is a design question not answered here.