Three numbers, and one of them decides everything
Footing tonnage is area times depth times density. Area in square feet, depth converted from inches to feet by dividing by twelve, and the product is cubic feet. Multiply by pounds per cubic foot and divide by 2,000 and you have tons. A 100 by 200 ft arena at four inches is 20,000 square feet times a third of a foot, which is 6,667 cubic feet, or 247 cubic yards. At 100 lb per cubic foot that is 667,000 lb, which is 333 tons.
Area and depth are things you can measure. Density is not, and it is where the answer is won or lost. Washed sand runs around 100 lb per cubic foot loose. A sand and fibre blend runs lighter, perhaps 85. A sand and rubber blend lighter again, around 70. Rubber crumb on its own can be as low as 35. That is a range of nearly three to one for the same arena at the same depth: 333 tons of sand against 117 tons of crumb. Order the wrong one by weight and you either bury the arena or barely dust it.
The generic figures in the material list are orientation, not specification. Loose delivered density varies with gradation, moisture and the specific source, and the supplier knows theirs. Ask for it, enter it in the density field, and every other number on this page follows correctly. If a supplier quotes by the cubic yard instead of the ton, the page prints the tons-per-yard conversion so you can compare the two quotes on the same basis.
Why the order is larger than the arena
The settlement allowance defaults to eight percent, and it is covering three separate things that all point the same direction.
| What eats material | Roughly |
|---|---|
| Compaction under traffic once the surface is ridden | A few percent of the loose depth |
| Uneven spread — thin at the ends, deep on the track | Whatever the grading tolerance is |
| Material lost into an unsealed or coarse base | Depends entirely on the base |
| Scale ticket variance and what stays in the truck | Small but never zero |
The asymmetry is what matters. Coming up short means a second haulage charge for a fraction of a load and a surface that rides differently in the middle than at the ends until it is fixed. Ordering eight percent extra means a small pile at the side of the arena that gets spread into the track over the first month, which is where you want the extra anyway.
The base is a different question
This calculator sizes the footing layer, meaning the loose material you ride on. It says nothing about the base course underneath, the compaction of the subgrade, the drainage, or the grade the whole thing sits at, and those decide whether the footing behaves at all. Footing spread over a base that holds water is footing that will be ruined by the first wet month regardless of how correctly you calculated the tonnage.
The excavation and grading side of that has its own arithmetic. The cut and fill calculator handles the earthwork balance, the excavation volume calculator covers the dig, and the gravel driveway calculator does the base course in exactly the same area-times-depth-times-density way this page does. For setting out the rectangle square before any of it, the site layout squaring calculator gets the diagonals right.
Topping up an existing arena
The most common use of this page is not building an arena, it is adding an inch to one that has thinned. Enter the depth you want to add rather than the total depth you want to end up with, and the answer is the top-up. The tons-per-inch figure in the delivery section is there for exactly this: it tells you what a single inch across your surface costs in tons and in money, which turns a vague plan to add some more sand into a decision with a number attached.
What it will not tell you is how deep the footing should be. That is a riding-surface judgement that depends on the discipline, the material, the base and the horses using it, and it is made with whoever built or advises on the arena. Deeper is not automatically better, for the horses or for the base. The calculator has an opinion about volume and no opinion at all about the surface.
Questions people ask
How many tons of sand does an arena need?
Area in square feet times depth in feet times density in pounds per cubic foot, divided by 2,000. For a 100 by 200 ft arena at four inches with sand at 100 lb per cubic foot, that is 20,000 x 0.333 x 100 / 2,000, which is 333 tons before any settlement allowance. A 20 by 60 metre dressage arena, about 66 by 197 ft, works out at roughly 217 tons at the same depth and density. Change the density and the answer changes proportionally, which is why the supplier figure matters more than the arithmetic.
Why does the material I choose change the tonnage so much?
Because tonnage is volume times density, and footing materials differ in density by nearly three to one. The arena needs a fixed volume, set by its area and the depth you want. Filling that volume with washed sand at about 100 lb per cubic foot takes roughly three times the weight of filling it with rubber crumb at about 35. Blends land in between. This is also why comparing two quotes only works when both are on the same basis: a price per ton for a light material and a price per ton for a heavy one are not comparable until you convert both to the tons your volume actually requires.
Should I order by the ton or by the cubic yard?
Whichever the supplier quotes, but convert so you are comparing like with like. Volume is what the arena needs and weight is what the truck carries, and the bridge between them is density. The page prints tons per cubic yard for the density you entered, so a yard quote and a ton quote can be put side by side. Be aware that moisture content moves weight and not volume: material delivered wet weighs more per yard than the same material dry, so a ton-priced load of wet sand delivers less volume than a ton of dry. If the quotes are close, ask which basis the supplier prefers and why.
How deep should arena footing be?
Not a question this page answers, and the depth field is deliberately an input rather than a suggestion. Footing depth is a riding-surface decision that depends on the discipline, the specific material and its gradation, the base beneath it, drainage and the horses using it, and it is made with whoever is building or advising on the arena. Deeper is not automatically better; too deep is its own problem for the surface and for the base. What the calculator contributes is the cost of the decision, in tons per inch, so the conversation about depth happens with the tonnage in front of you.
Can I calculate a round pen the same way?
Yes, and the shape selector does it. The only change is the area: a circle is pi times the radius squared, so a 60 ft round pen is pi times 30 squared, which is 2,827 square feet. Everything after that is identical — multiply by depth in feet for cubic feet, by density for pounds, divide by 2,000 for tons. A 60 ft pen at four inches of sand at 100 lb per cubic foot comes to about 47 tons, which is two or three loads rather than the fifteen a full arena needs. The same settlement allowance applies, and the base underneath matters just as much on a small circle where traffic concentrates on one track.