Stone Calculator: From a Grade Number to a Ton Figure
Enter your project dimensions
A downspout run on a flat Anne Arundel lot ends in a trench, and the trench is where most Maryland drainage jobs turn into a number. Say it is 46 feet long, 18 inches wide and dug 14 inches deep, to be filled with washed #57. That footprint is 69 square feet. Fourteen inches is 1.1667 feet, so the volume works out at 80.5 cubic feet, which divides down to 2.98 cubic yards. At the published weight for that grade, 1.40 tons to the yard, the order is about 4.2 tons, and with the 5 percent box ticked the stone calculator reads 3.13 cubic yards and 4.4 tons. Call it 4.5 tons on the listing. The trench is invented for this page, but the working is the working.
Why nobody subtracts the pipe
A 4-inch pipe down the middle of that trench takes up about 0.15 of a cubic yard over the full 46 feet, which is a wheelbarrow and a half. Calculate the whole trench, order the whole trench, and let the pipe be the reason you have a little spare at the outfall. Anything under 6 inches in diameter is not worth taking off the total.
Line the trench with non-woven fabric before the stone goes in, wrapped up and over the top once it is filled. Coastal Plain ground is unconsolidated sand, silt and clay, and every one of those will migrate into open stone and close the voids the drain depends on.
Grade numbers on a plan, product names in the select
The form starts with a shape. Rectangle takes a length and a width in feet and covers a pad, a drive or a trench run. Circle asks for a diameter across the widest point. Multiple areas holds up to five pieces at once, which is how a foundation drain that turns two corners goes in without three separate calculations.
Depth goes in as inches and the box accepts 0.25 up to 24, which is enough for every layer on this page bar a very deep trench. Where a trench runs deeper than 24 inches, split the depth across two areas and add the results, exactly as you would for a wall backfill. Pick the material next, since that selection sets the weight the tool converts with, then decide on the box marked add 5 percent extra for compaction and spillage. Cubic yards, tons and cubic feet all come back together, and the result can be emailed across as a written quote.
Depth by what the layer is doing: 2 to 3 inches for a top course over an existing surface, about 4 inches for a base, and 12 inches or more inside a French drain.
What the three figures tell you with the trench already open
Cubic yards is the excavation. It is the figure that tells you how much spoil is going out and how much space there is to fill, which on a trench job is the number you plan the day around. Tons is what crushed stone is sold by, so that is the entry for the quantity box. Cubic feet is for the last stretch: a builder's wheelbarrow holds around three of them, so a 12-cubic-foot shortfall is four trips rather than another delivery.
To check the arithmetic yourself, multiply the two dimensions in feet for square footage, divide the depth in inches by twelve and multiply it through for cubic feet, divide by twenty-seven for cubic yards, and multiply by the weight for your grade.
Angular stone settles 5 to 10 percent, so order past the line
Clean angular material loses somewhere between 5 and 10 percent of its loose height once traffic or a compactor has been over it. The 5 percent box on the form is aimed at that ordinary settling and at what gets spilled on the way, and it is worth ticking for most jobs. What it does not do is substitute for a specified compacted depth: on engineered base work, dig and order to the compacted figure on the drawing and let the loose material sit proud.
Round up rather than down. Half a ton of #57 left over fills ruts after a thaw, tops a settled drive edge or beds a downspout splash area, and none of that is true of a part-load delivery booked three weeks later for one job.
Clean stone or stone with fines, and what each yard weighs
Everything on this page falls on one side of a single line. Washed, clean grades leave voids between the pieces, so water moves through them and they never bind: that is drainage stone. Graded blends carry dust, which packs the voids and locks the layer together under rolling: that is base. The two are not alternatives. Fines in a French drain will clog it, and clean stone under a paver base will keep moving for years.
| Grade, and where it usually lands on a Maryland job | Published weight per cubic yard | Tons per yard |
|---|---|---|
| #57, #67 or 3/4 inch stone, in foundation drains and over drives | about 2,800 lb | 1.40 |
| #8, #89 or 3/8 inch chips, in paver joints and finish layers | about 2,800 lb | 1.40 |
| Screenings, called stone dust in Maryland yards, screeded under flagstone | about 2,900 lb | 1.45 |
| #4 stone and railroad ballast, on entrances and equipment tracks | about 2,900 lb | 1.45 |
| CR-6 and crusher run, compacted under a drive or pad | about 3,000 lb | 1.50 |
| RipRap, armoring a tidal bank or a culvert outlet | about 3,100 lb | 1.55 |
Those are approximate figures from this site's own published chart. The grade numbers behind them run backwards to intuition: the lower the number, the bigger the rock. #4 is 3/4 to 1-1/2 inches, #57 is 3/16 to 1, #67 is 1/4 to 3/4, #8 is around 3/32 to 3/8, and #89 runs from 3/8 inch down into fines. Railroad ballast is heavy angular rock from 1 to 2.5 inches, used where load and fast drainage both matter.
This is the page for a job where the grade has already been decided, by a plan, a permit or a contractor. If you are still choosing a material by what the job is rather than by a number, start on the gravel calculator instead, and take base quantities to the road base calculator.
Once the tonnage is settled, open the product page for the grade you selected, set the quantity and choose a delivery date. Delivery is arranged at checkout from the ZIP code you enter, and the truck needs firm, clear ground to tip on.
Common questions
The trench is open and the delivery comes up short. What then?
An open trench does not wait well: rain washes the sides in and a partly filled drain has to be raked out before the rest goes on top. That is why the sensible cushion goes on the first order rather than the second. If it does happen, fill from the outfall end back toward the house so the working section stays the part you can still reach, and cover the open run if weather is coming.
How close is the estimate on a trench dug by hand?
The arithmetic is exact; the hole is not. A hand-dug trench is never the same width at the bottom as at the top, and a machine-dug one is usually wider than the drawing. Measure the width you actually cut in two or three places and use the average. On a 46-foot run at that depth, every extra inch of width adds about 0.17 of a cubic yard, so a trench cut two inches wide of the drawing is a third of a yard light.
The drawing specifies #57. Where does that turn into an order?
On the listing for that grade, since the catalog is organized by the numbers themselves: a plan calling for #57 goes to the #57 Stone page and one calling for #8 goes to #8 Crushed Stone. Where the paperwork says 3/4 clean, that is the same rock as #57 in most Maryland yards. All of these grades are traded by the ton, so the figure from the form drops straight into the quantity box, and the date is chosen on the same page.
Where should four and a half tons of angular stone go on a narrow suburban lot?
Somewhere firm, clear overhead, with room for a truck to back in and tip, and as close to the trench as the access allows. Angular stone stays where it is put rather than rolling out like rounded material, so the pile takes less ground than you expect. Put a tarp down if it has to land on a drive or an apron, and keep it off the line you will be wheelbarrowing along.
The form gives yards and tons together. Which is the one to work from?
Both, for different parts of the day. Yards is the volume, so it tells you what you are digging out, whether the spoil fits on a tarp and whether two jobs can share one load. Tons is the trading unit for crushed stone, so it is the number that goes on the order. Keep the yard figure written down; it is the one that makes sense of the pile in the drive.
Related calculators
Spec'd it? We stock it.
Twelve graded stone products, priced per ton, free delivery across Maryland.
