Two capacities, and only one of them is obvious
A trailer has a volume and it has a payload, and they are unrelated numbers that happen to belong to the same object. The volume is easy to see — you can look at the deck and the sides and estimate it within a few percent. The payload is a figure on a plate that nobody looks at while a loader bucket is swinging overhead. Which one you run out of first depends entirely on what you are hauling, and the answer flips completely between the two ends of the material range.
A 5 by 8 foot trailer filled 18 inches deep holds about 2.2 cubic yards. Filled with bark mulch at roughly 600 lb per cubic yard, that is around 1,300 lb, and a trailer with 2,000 lb of payload takes it comfortably. Filled with crushed stone at around 2,700 lb per cubic yard, the same volume is 6,000 lb — three times the payload, in a trailer that still looks like it has room in it. The stone runs out of pounds at about 8 inches of depth, which is less than half the height of the sides.
That is the whole point of this page. With dense material the sides of the trailer are not a capacity indication, they are a trap, and the visual cue everybody uses is the wrong one.
What the numbers actually are
| Material | Roughly, lb per cubic yard | What moves it |
|---|---|---|
| Gravel, crushed stone | 2,400 to 2,900 | Stone type, size, how wet, whether it is screened |
| Sand, dry | 2,400 to 2,700 | Grain size and how tightly it has settled |
| Sand, wet | 2,900 to 3,400 | Water alone can add several hundred pounds a yard |
| Topsoil, dry and screened | 2,000 to 2,200 | Organic content — more organics, lighter |
| Topsoil, wet | 2,700 to 3,200 | Rain the night before changes the load substantially |
| Clay and heavy fill | 2,800 to 3,400 | Clay holds water and does not give it up |
| Bark mulch | 400 to 800 | Bark type, particle size, moisture — the widest range of all |
| Compost | 900 to 1,200 | How finished it is and how wet |
| Wood chips | 600 to 900 | Green chips are far heavier than dry |
| Firewood, stacked seasoned | 450 to 900 | Species dominates; moisture content next; loose thrown is lighter per yard than stacked |
Every one of those is a range because the material is a range. Nobody sells a cubic yard with a certified density, and the number changes with the weather. Treat the midpoints as planning figures, load below the calculated limit rather than to it, and weigh a representative load once so that you know what your supplier material actually does.
Firewood deserves a separate note because it is sold by the cord rather than the yard. A cord is 128 cubic feet stacked, which is about 4.74 cubic yards, so a cord of seasoned hardwood at 800 lb per stacked yard is around 3,800 lb. That is more than the payload of a great many trailers, which is why firewood tends to arrive in halves and thirds. Green wood can be half as heavy again as seasoned, and the species range is enormous — dense oak and hickory against light pine and poplar is close to a factor of two. If the trip is about firewood specifically, the firewood cord calculator works the volume side out properly.
Working with the loader operator
The practical problem is that the person with the bucket is judging by eye and their eye is calibrated to trucks, not to your trailer. A few things help.
- Ask for it by weight where the yard sells that way. Many do, and a ticket in pounds removes the guessing entirely.
- Mark the depth. A line of tape or paint on the inside of the trailer at the calculated depth gives the operator a target that means something.
- Ask for one bucket at a time. Loader buckets are commonly around a yard, sometimes more, and a single scoop can be most of a small trailer payload.
- Load over the axles, slightly forward. Loose material dumped at the back is a tongue weight problem before it is anything else — see the tongue weight calculator.
- Say no when it is already enough. Nobody at the yard is going to be offended, and nobody at the yard is responsible for the trailer.
The other half of the job is what happens after the load is on. Loose material has to be covered — a tarp is not optional at highway speed, stone that comes out of an open trailer arrives at a windscreen behind you, and the same trip that spills half a yard of mulch has also emptied the load you paid for. Once loaded, the axle side of the arithmetic is on the trailer axle load calculator, and the material quantities for what you are building with it are on the gravel driveway calculator, the topsoil calculator and the mulch calculator.
Questions people ask
How much gravel fits in a 5 by 8 trailer?
Fits and can be carried are different questions, and with gravel they are wildly different. A 5 by 8 deck filled 18 inches deep holds about 2.2 cubic yards of space, which at roughly 2,700 lb per cubic yard would be about 6,000 lb of stone. Very few small utility trailers have anything close to that payload; 2,000 lb is a common figure, and 2,000 lb of gravel is about three quarters of a cubic yard, or roughly 8 inches deep across that deck. So the honest answer is that a 5 by 8 trailer holds two and a bit yards of gravel and can carry three quarters of one. Take the payload from your trailer plate minus the trailer weighed empty, divide by the density, and load to that. If you need more, make more trips or have it delivered — delivery is usually cheaper than a set of axles.
Is a cubic yard of soil heavier than a cubic yard of gravel?
Usually not, but wet soil closes the gap and heavy clay can overtake ordinary gravel. Dry screened topsoil runs roughly 2,000 to 2,200 lb per cubic yard against gravel at roughly 2,400 to 2,900, so dry soil is lighter. Add water and that reverses fast: wet topsoil can reach 2,700 to 3,200, and damp clay-heavy fill can be over 3,000. Since soil sits in an open pile at a yard and absorbs whatever fell on it, the density of what you are being loaded with depends on the weather in the preceding week. This is the main reason the calculator shows a range as well as a midpoint, and the reason to load short of the calculated figure after rain rather than to it.
Does the material heap above the sides count?
It counts as volume, it counts as weight, and it counts against you twice over. A heaped load adds material at the top, which is exactly where added weight does the most damage to the stability of the trailer, and it is the material most likely to leave the trailer on the road. Anything heaped also has to be covered properly, since a tarp over a heap is harder to secure than a tarp over a flat load. The heap field exists here so you can see what the extra costs you in pounds, and the usual right answer is to keep the load below the sides and take a second trip. If the reason for heaping is that the trailer is space-limited rather than weight-limited, a taller side extension is the equipment answer, but the payload plate still governs.
How do I find my trailer payload capacity?
Take the GVWR from the trailer plate and subtract what the trailer actually weighs empty, weighed on a scale as it stands today with its ramps, spare, toolbox and anything else somebody bolted on. The result is what is left for cargo. Do not use the brochure empty weight, which was measured before the trailer accumulated its additions, and do not use the axle ratings, which add up differently and do not describe the ceiling. Public scales at grain elevators, landfills and recycling yards will weigh a trailer for a few dollars. That one weighing gives you a number you will use for every load afterwards, and it is worth writing on the trailer with a paint pen so it is there when you need it.
Should I buy by the yard or by the ton?
Whichever way the yard sells it, but understand what you are being given. Sold by volume, you get a bucket count and the weight depends on how wet the pile is that day, which means the same order can be several hundred pounds heavier after rain. Sold by weight, the ticket tells you exactly what is on the trailer, which is the number that matters for the plate, but the volume you get for a ton varies the same way in reverse. For calculating how much material a job needs, volume is the useful unit and the material calculators here work in cubic yards. For deciding what to put on the trailer, weight is the useful unit. If the yard can give you a weight ticket, take it — it settles the only question that has a legal and mechanical consequence.