The Short Answer for 300 Square Feet
A 300 square foot rock garden covered in small decorative stone needs about 2.5 tons at 2 inches deep. Go to 3 inches deep and you are at about 3.8 tons. If that is the only thing you came here for, write it down and go order.
Those numbers assume the stone most people actually use as ground cover in a rock garden, roughly half an inch to 2 inches across. Pea size gravel, small river rock, crushed decorative stone, that family of material.
The figure moves for two reasons and two reasons only. How deep you spread it, and how big the individual stones are. The rest of this article is an explanation of those two variables and how to keep them from surprising you at the checkout counter.
The rule of thumb underneath the math is worth memorizing because it works on any bed size. One ton of small decorative stone covers about 120 square feet at 2 inches deep, and about 80 square feet at 3 inches deep. Divide your square footage by those coverage numbers and you have your tonnage in about four seconds. For 300 square feet that is 300 divided by 120, or 2.5 tons.
One thing to flag right away. Accent boulders are not part of this tonnage. They get bought and budgeted separately, and we cover why further down.
Measuring an Irregular Bed Without Overthinking It
Almost nobody has a rectangular rock garden. They curve around a downspout, wrap a corner of the house, or flow along a walkway in a long sweep. That is fine. You do not need a precise area, you need a number close enough that you order the right amount of stone.
Break a curved bed into rectangles
The most reliable field method is to stop treating the bed as one shape. Divide it into two or three rectangles and maybe a triangle at the tapered end. Measure each piece, multiply length by width, and add the results together. A triangle is base times height divided by two.
Walk the bed with a tape measure or a rope marked at one foot intervals. Sketch the shape on a scrap of paper and write each measurement directly on the sketch as you take it. Trying to hold six numbers in your head while you walk back to the garage is how people end up a ton short.
The eyeball method for a kidney shape
Kidney and teardrop beds are common in front yards and they look harder to measure than they are. Take the longest length end to end, take an average width by measuring at a few points along that length, and multiply the two. That product will run a little high because of the pinched section where the bed narrows, so treat it as your upper number and order against it rather than trying to shave it down by eye.
Two other shapes come up often enough to be worth having on hand. A circle is radius times radius times 3.14. A rough oval is average length times average width times 0.8.
Round up slightly whenever you are measuring curves. Leftover stone has uses. A delivery that is half a ton short does not, and nobody wants to pay a second delivery fee to finish a strip along the back edge.
Why 300 square feet is bigger than people picture
Three hundred square feet sounds modest until you stand in it. That is a bed 15 feet by 20 feet. It is also a border 5 feet wide running 60 feet along a fence line, which is a serious stretch of yard.
This matters because people tend to eyeball low. A bed that feels like a weekend project on paper turns into several tons of material that has to be moved one wheelbarrow at a time. Measure before you plan the weekend.
Picking Your Depth, and Why 2 to 3 Inches Is the Target
For decorative stone used as ground cover, 2 to 3 inches is the working range. Thin enough that you are not buying stone for the sake of it, thick enough to hide the soil or fabric underneath and stay looking full.
Go under 2 inches and the problems show up fast. You see dirt through the gaps, light reaches the soil so weeds get a foothold, and within a season of settling and foot traffic the bed reads thin and patchy. Stone always shifts. A skimpy layer has nowhere to shift to.
Go over 3 inches and you are paying for material that nobody will ever see. Deep loose stone is also genuinely unpleasant to walk across and a nuisance to rake clean when leaves pile up in fall.
The exception is larger material. River rock and medium stone generally want 3 to 4 inches because the individual pieces are bigger and need that depth to sit level instead of rocking around on top of each other. One large stone sitting proud of a shallow layer looks like a mistake.
Some rock gardens are built over a crushed stone drainage base, typically 4 to 6 inches of it under the decorative layer. If that is your plan, calculate that base as its own separate volume. Most simple ornamental beds on reasonably draining ground do not need one, so do not add the cost unless you have a drainage reason.
One practical note. Depth gets judged after the stone settles, not on dump day. A fresh pile spread loose will tighten up as it rains and as you walk on it. Plan for the finished look.
The Math, Square Feet to Cubic Yards to Tons
Here is the whole calculation in one line. Length times width times depth in feet, divided by 27, equals cubic yards. The divide by 27 step is just converting cubic feet into cubic yards, because there are 27 cubic feet in a yard.
Step one, find cubic yards
The only trick is that depth has to be in feet, not inches. Divide inches by 12. To save you the arithmetic, here are the three you will actually use.
- 2 inches is 0.167 feet
- 3 inches is 0.25 feet
- 4 inches is 0.333 feet
If you already know your square footage, skip the length times width part and multiply square feet by the depth decimal, then divide by 27.
Step two, convert yards to tons
Decorative stone runs roughly 1.3 to 1.4 tons per cubic yard. Use 1.35 as your working number and you will land on the same answers the coverage rule of thumb gives you.
Why two units at all? Stone is sold by weight because that is what a truck scale measures and what the loader can verify. But volume is how you think about a garden bed, since what you care about is covering an area to a depth. Any stone yard will work from either number, so give them whichever one you calculated and tell them the depth you are targeting.
The 300 square foot example, worked out
At 2 inches deep, 300 times 0.167 equals about 50 cubic feet. Divide by 27 and you get about 1.85 cubic yards. Multiply by 1.35 and you land at about 2.5 tons.
At 3 inches deep, 300 times 0.25 equals 75 cubic feet. Divide by 27 and you get about 2.78 cubic yards. Multiply by 1.35 and you land at about 3.8 tons.
Those are the numbers to read off to a supplier. If you would rather not run it by hand, or you want to test a couple of depths before committing, our stone calculator does the same arithmetic in a few clicks.
Either way, build in a small overage. No bed is perfectly even, low spots eat more material than you expect, and stone settles into soil over the first few weeks. A modest cushion on the order is normal practice, not padding.
Bigger Stone Covers Less Ground
This is the single most common budgeting mistake in rock garden projects, and it catches experienced DIY gardeners as often as first timers. A ton is a measure of weight, not coverage. Coverage drops hard as stone size goes up, and it drops faster than most people assume.
The reason is simple once you see it. Bigger stones leave bigger air gaps between them, and each piece forces a deeper effective layer because the layer cannot be thinner than one stone. The same weight of material ends up spread across much less ground.
For your 300 square foot bed, switching from small decorative gravel to 2 to 4 inch rock roughly doubles your tonnage. The same bed, the same depth target, double the order. That is a real budget swing and it is worth deciding before you fall in love with a sample in the yard. Go up again to 4 to 8 inch rock and coverage per ton falls to roughly a third of what small stone gives you.
The design move that keeps orders sensible is to use small stone for the bulk of the field and save larger stone for texture. A band of bigger rock along a dry creek line, a cluster at the base of a planting, an edge treatment where the bed meets lawn. You get the varied look without paying field rates for the heavy material.
If you are mixing two sizes, calculate each zone separately. Do not average the whole bed. Measure the square footage of the large stone area, run it at its own coverage rate, then run the remaining area at the small stone rate and add the two.
Budgeting Accent Boulders Separately
Boulders are the part of a rock garden the tonnage formula does not handle at all. They are generally sold by the piece or by the pound rather than folded into bulk coverage math, and they are the element that gives a rock garden structure instead of looking like a parking strip.
They sit outside the calculation because they are placed, not spread. A boulder takes up footprint in the bed and displaces the ground cover that would otherwise sit there, but there is no coverage rate for a single object you set down by hand or with a machine.
The practical sequence is to decide boulder count and rough sizes first, get them placed, then measure the remaining open area for your ground cover tonnage. If you are planning on paper instead, subtract each boulder footprint from your square footage first. A boulder roughly 3 feet across covers about 7 square feet of ground, so three of them take about 20 square feet off a 300 square foot bed before you run the formula.
On sizing, trust this. Boulders look smaller outdoors than they do in a stone yard, where everything sits in a tight row against a fence. Most homeowners pick too small and end up with a bed that reads as scattered rubble. One or two genuinely large anchor stones do more for a 300 square foot garden than eight medium ones.
Anything beyond what two people can safely roll needs equipment, and equipment needs a path to the bed. Confirm access, gate widths, and exactly where each stone is going before the delivery shows up. One more detail separates a good looking rock garden from an obvious one. Bury the base of each boulder a few inches into the soil. A stone sitting on top of the gravel looks dropped.
Ordering, Turning Your Number Into a Delivery
When you order, give three pieces of information. The material and size you want, the total tons or cubic yards, and the depth you are targeting. That last one lets the yard sanity check your math before a truck gets loaded.
Buy bulk for a bed this size. Covering 300 square feet with bagged landscape rock means hauling, opening, and disposing of a punishing number of bags, and bag coverage is small enough that most people underbuy twice before giving up. Bagged stone makes sense for a planter or a small repair, not for a project at this scale. Round up to a sensible bulk order rather than asking for an exact fraction of a ton. Leftover stone fills low spots and handles the touch ups you will want next spring.
Before the truck arrives, have a dump spot picked out. A hard surface as close to the bed as you can manage, with a tarp down first if the driveway finish matters to you. The closer the pile, the shorter every trip, and there will be a lot of trips. A wheelbarrow and a flat rake handle the job fine, but be realistic about volume. Several tons of stone is a full day of moving for one person, and loaded barrows of rock are far heavier than the same barrow of mulch.
Do all your prep before the pile shows up. Edge the bed, remove existing growth, grade the soil, and lay fabric if you are using it. Then come back to your two numbers. Small decorative stone at 2 inches puts a 300 square foot bed at about 2.5 tons, and 3 inches puts it at about 3.8 tons. Any other bed size is the same move, divide your square footage by the coverage per ton for the stone you picked.
How We Started
We started Mulch Mound because we got tired of the hassle that came with buying landscaping materials. The options were either loading bags into your car at a garden center or calling around to local suppliers, trying to figure out pricing, minimums, and delivery schedules. Neither option felt convenient or transparent.
Three of us – Alec, Mo, and Tyler – decided there had to be a better way. Alec and Tyler got their start back in 2013 running a landscaping business during college, moving mulch and mowing lawns to pay tuition. That experience taught them how frustrating it was to source materials, and years later, that frustration turned into Mulch Mound.
We focus on making it simple to get mulch, stone, and soil delivered directly to your home. Order online, pick your delivery date, and we handle the rest. No loading bags. No calling multiple suppliers. No wondering if you bought enough or paid a fair price.
We work with quality local suppliers in the areas we serve and aim to be straightforward about what we offer and what it costs. Landscaping is hard work. Buying the materials for it shouldn't be.
Frequently asked questions
How can I check that a stone delivery was the right amount?
Ask for the weight ticket. Bulk yards weigh the loaded truck and the empty truck, and the difference is what you bought, so the ticket is the record of what actually landed in your driveway. Keep it until the bed is finished.
The second check is the bed itself. Once the stone is spread, push a screwdriver or a stick straight down in a few spots and see where it hits soil or fabric. If you ordered for 2 inches and you are reading an inch and a quarter across most of the bed, you either spread it over more area than you measured or you are short. That is a far more useful test than eyeballing the pile on delivery day, because loose stone in a heap always looks like more than it is.
How many tons is one cubic yard of river rock?
Roughly 1.3 to 1.4 tons. Washed, wet, or dense stone sits at the heavy end of that range, while drier angular material tends to sit lighter because the irregular shapes trap more air between pieces.
This is also why two deliveries of the exact same product can weigh differently. A pile that sat through two days of rain before loading carries water weight, so you get slightly less actual stone per ton. It is not worth losing sleep over on a home project, but it explains small gaps between what you calculated and what covered your bed.
Do I need landscape fabric under a rock garden?
It helps early and it is not a cure. Fabric blocks existing weeds from pushing up through the stone for the first few seasons, which is real value. What it cannot do is stop seeds that blow in and land on top. Those germinate in the fine debris that collects between stones over time, rooting above the fabric entirely.
Treat it as a maintenance tradeoff rather than a requirement. Fabric buys you easier early years and makes the stone easier to remove later if you change the bed. It also makes spot digging and future planting more annoying. Either choice is defensible, but neither one means never weeding.
Can I put rock over an existing mulch bed?
Pull the old mulch out first. Wood mulch keeps breaking down whether there is stone on top of it or not, and as it decomposes it turns into a soft, uneven layer. The rock above it sinks into the soft spots, so the bed develops dips and the stone starts disappearing into the mix.
Rake or shovel the mulch off down to soil, grade it flat, then start your stone layer. The old mulch is not wasted. It composts fine or goes around trees elsewhere in the yard.
How do I estimate a dry creek bed instead of a flat bed?
Measure the cross section rather than assuming a single depth. Dig or picture the channel profile, measure the depth at the center and at a point partway up each bank, and average those readings. Use that average in the same formula you would use for a flat bed, with the width measured bank to bank. Stone sizing follows the body section above, so run each size zone on its own coverage rate.