Coverage is depth first, density second
A ton of gravel is a weight, and coverage is an area times a depth. The bridge between them is density, and it produces two separate effects that people often collapse into one:
cubic yards per ton = 1 ÷ tons per yard
square feet per ton = cubic yards × 27 × 12 ÷ depth (in)
= 324 ÷ (tons per yard × depth)
The depth is in the denominator, so it dominates: doubling the depth halves the coverage, whatever the stone. The density sits beside it and shifts the answer by around 11 percent across the materials a yard actually stocks — 1.35 tons per cubic yard for river rock up to 1.5 for dense-grade base.
A ton of crushed stone at 1.45 tons per cubic yard is 0.69 cubic yards. Spread that at 3 inches — a quarter of a foot — and it covers 0.69 × 27 ÷ 0.25, which is 74.5 square feet. The same ton of river rock at 1.35 is 0.74 cubic yards, and covers 80.
Chart: square feet per ton, by material and depth
Four materials at the three depths that cover most jobs. The lightest stone is first, because light stone is the one that covers the most area per ton.
| Material | Tons / cu yd | At 2 in | At 3 in | At 4 in |
|---|---|---|---|---|
| River Rock / Smooth Pebble | 1.35 | 120.0 | 80.0 | 60.0 |
| Pea Gravel (3/8") | 1.4 | 115.7 | 77.1 | 57.9 |
| Crushed Stone #57 | 1.45 | 111.7 | 74.5 | 55.9 |
| Crusher Run / Dense Grade Base | 1.5 | 108.0 | 72.0 | 54.0 |
Each figure is the area where one ton really is one ton — the gravel calculator returns 1.0 ton for a one-foot-wide strip that long. In practice you go the other way: measure the area, fix the depth, divide, and round up.
The depth is the whole decision
Because depth sits in the denominator, it changes the order faster than the material does. One ton of crushed stone, at four depths:
| Depth | Coverage per ton |
|---|---|
| 2 in | 111.7 sq ft |
| 3 in | 74.5 sq ft |
| 4 in | 55.9 sq ft |
| 6 in | 37.2 sq ft |
Two inches is a decorative bed or a garden path. Three to four is a drive surface. Six is the base layer under pavers, and that row is why paver base always looks like an alarming tonnage: the same ton covers 37 square feet at 6 inches, a third of what it covers at 2.
Why three suppliers gave you three answers
A supplier quoting 100 square feet per ton and one quoting 120 are usually both describing their own stock. The difference is density: a ton of river rock is a larger pile than a ton of crusher run, and the pile is what covers ground.
The question worth asking is not “what does a ton cover” but “what does a yard of this weigh”. With that number and your depth, the coverage follows from the formula at the top of this page, and it will match what arrives on the truck.
Chart: same area, same depth, four tonnages
A 12 × 20 area at 3 inches is 60 cubic feet of stone whatever you fill it with. The tonnage is what changes, and it is the number on the order:
| Material | Tons | 50 lb bags |
|---|---|---|
| River rock | 3 t | 120 |
| Pea gravel | 3.2 t | 128 |
| Crushed stone #57 | 3.3 t | 132 |
| Crusher run | 3.4 t | 136 |
Four tenths of a ton — 16 bags — separate the lightest material from the heaviest over a 240 square foot area. That is the whole argument for knowing the density: the volume was never in question, and the tonnage never was either until you decided what to fill it with.
The mistakes that turn into a short load
01
Using the supplier's coverage number for a different stone
Coverage per ton is set by density. River rock at 1.35 tons per cubic yard covers about 11 percent more area per ton than crusher run at 1.5, because a ton of it is a larger pile. Ask what the stone weighs per yard, not what it covers.
02
Measuring the area and skipping the depth
Coverage is inversely proportional to depth, so a 3-inch bed covers two thirds of what a 2-inch bed does. Depth is the decision that sets the order, and it is the number most often left vague — 2 inches for a path, 3 to 4 for a drive, 6 under pavers.
03
Buying bags for a job measured in tons
A ton is 40 bags of 50 lb. At three tons that is 120 bags, which is several trips, a lot of plastic, and more handling than a bulk delivery. Bags make sense up to about a ton; past that the arithmetic argues for bulk.
04
Ordering the exact tonnage from a coverage figure
Coverage per ton is a planning figure, and grading, compaction, and spillage all consume stone. Round up to the next tenth of a ton at minimum, and expect a bulk delivery to be booked in whole or half yards rather than in exact tons.
05
Forgetting that compaction takes depth away
Loose stone settles. A 4-inch loose layer of crushed stone compacts to roughly 3 inches under a plate compactor, so a bed specified at 4 inches compacted needs to go down thicker than the finished dimension.
Turn your own area into tons
The link below opens the gravel calculator on a 12 × 20 area at 3 inches of crushed stone — 3.3 tons, or 132 bags of 50 lb. Change the depth to 2 and watch the tonnage drop; change the material and watch it move the other way with nothing about the area changed.
Laying a driveway rather than a bed? Gravel for a driveway works the same tonnage arithmetic through three layers instead of one, and gravel for a trench covers the narrow, deep case where the width is the surprise. Ordering by the ton instead of by the area? Cubic yards in a ton of gravel is the same density table read backwards.