How Much Gravel Do I Need? Formula, Tons, and Depth Chart

How much gravel do I need? Multiply your area in square feet by the depth in inches, divide by 12, then divide by 27. That gives cubic yards. A 10x20 ft driveway (200 sq ft) at 4 inches deep needs 2.47 cubic yards, which is roughly 3.5 tons. Run your own numbers in the Gravel Calculator: enter square feet and depth in inches, and it returns cubic yards plus an approximate tonnage.

How do you calculate gravel?

One formula covers every gravel job, from a flower bed to a full driveway:

• Cubic yards = area in square feet x (depth in inches / 12) / 27

Here is what each step does. Dividing the depth by 12 turns inches into feet, so all three of your measurements are in the same unit. Multiplying by the area gives cubic feet. Dividing by 27 converts cubic feet to cubic yards, because a cubic yard is 3 ft x 3 ft x 3 ft, which is 27 cubic feet.

Walk through the 10x20 driveway. The area is 200 sq ft. The depth is 4 inches, so 4 / 12 = 0.333 ft. Then 200 x 0.333 = 66.7 cubic feet. Divide by 27 and you get 2.47 cubic yards. That is the whole thing. No trick steps.

The math is simple, but it is easy to fat-finger a decimal at the supply yard. If you would rather not do it by hand, the Gravel Calculator does the same arithmetic and shows the tonnage next to it.

Worked driveway examples

All of these are 4 inches deep, a normal depth for a light residential surface layer:

• 10 x 20 ft (200 sq ft): 2.47 cubic yards, about 3.5 tons
• 20 x 20 ft (400 sq ft): 4.94 cubic yards, about 6.9 tons
• 10 x 50 ft (500 sq ft): 6.17 cubic yards, about 8.6 tons
• 12 x 100 ft (1,200 sq ft): 14.81 cubic yards, about 20.7 tons

Notice the pattern. Double the area, double the gravel. Double the depth, double the gravel. Nothing about this scales strangely, so once you have one number you can eyeball the rest. For a deeper look at driveway sizing, including base layers, see our guide on how much gravel you need for a driveway.

How do you measure the area first?

Everything downstream depends on getting square footage right. For a rectangle, length x width. A 12 ft wide driveway that runs 100 ft is 1,200 sq ft. Measure the real width, not the width you think you poured. Driveways wander.

For odd shapes, break the space into rectangles and add them together. A driveway with a parking apron off the side is just two rectangles. A curved bed can be measured as a rectangle that roughly covers it, then trimmed by eye. Precision to the inch is wasted effort here, because you are going to round up when you order anyway.

Circles need a different move: multiply the radius by itself, then by 3.14. A fire pit ring with a 5 ft radius is 5 x 5 x 3.14 = 78.5 sq ft.

If you are stitching several shapes together, the Square Footage Calculator handles the adding for you. Then carry that number into the gravel formula.

• Rectangle: length x width
• Circle: radius x radius x 3.14
• Triangle: base x height / 2
• Odd shape: split into rectangles, add the results

How deep should gravel be?

Depth is driven by what will sit on top of the gravel. Foot traffic needs very little. A pickup truck needs a lot more. Use these as starting points:

• 2 to 3 inches: decorative beds, borders, garden paths
• 4 inches: a light residential driveway surface
• 6 inches or more: heavier traffic, delivery vehicles, equipment
• 12 to 18 inches: a full driveway build, placed in several layers

That last line surprises people. A driveway built from bare dirt is not one 4 inch pour. It is typically 12 to 18 inches of material in stacked layers: a coarse base at the bottom, a middle layer, then a finer surface layer that you actually see and drive on. Each layer gets compacted before the next goes down.

So which number do you use? If you are topping up an existing driveway that already has a base, calculate at 4 inches. If you are building from scratch, calculate each layer separately and add them. Guessing here is the single most expensive mistake in the whole project. Our breakdown of how deep a gravel driveway should be covers the layer stack in detail.

Going too shallow costs you more in the long run than going too deep. Thin gravel over soft ground shoves sideways, ruts, and mixes into the dirt underneath. Then you buy it twice.

How many tons of gravel do I need?

Here is the annoying part of gravel shopping. You calculate in cubic yards. Most suppliers sell by the ton. So you have to convert, and the conversion depends on the material.

As a working average for estimating, 1 cubic yard of gravel weighs about 1.4 tons (roughly 2,800 lb). Going the other way, 1 ton is about 0.71 cubic yards. That average is good enough to plan with:

• 1 cubic yard = about 1.4 tons
• 2 cubic yards = about 2.8 tons
• 3 cubic yards = about 4.2 tons
• 5 cubic yards = about 7.0 tons
• 10 cubic yards = about 14.0 tons

Now the honesty part. That 1.4 figure is not a law of physics. Density varies by material, roughly 1.2 to 1.7 tons per cubic yard across common aggregates. Stone type, particle size, and how wet the pile is all move the number. Dense crushed stone sits at the high end. Lighter washed or decorative rock sits lower.

So use 1.4 to plan, then confirm the density with your supplier before you order. They know exactly what their product weighs per yard, and a one-minute phone call beats a wrong delivery. Ask them: how many tons per cubic yard for this specific material? Then redo the multiplication with their number.

Once you have your cubic yards, drop them into the Gravel Calculator for an approximate tonnage to bring to that call. For the full conversion picture, read how many tons of gravel are in a cubic yard.

Why do suppliers sell by weight at all? Because a truck scale is objective and fast. Volume in a dump bed is squishy: it depends on how the load settles and how wet it is. Weight does not lie. Prices vary a lot by region and by material, so quote your local yard rather than trusting a number from the internet.

How much area does a ton of gravel cover?

If you are thinking in tons already, flip the math around. One ton covers this much ground:

• 2 inches deep: about 116 sq ft
• 3 inches deep: about 77 sq ft
• 4 inches deep: about 58 sq ft
• 6 inches deep: about 39 sq ft

This is the fastest sanity check there is. Got a 500 sq ft driveway at 4 inches? Divide 500 by 58 and you land near 8.6 tons, which matches the worked example above. The two paths agree.

Watch how fast coverage drops as depth grows. Going from 2 inches to 4 inches cuts your coverage in half. Going to 6 inches cuts it by roughly two thirds. That is why the depth decision drives the budget more than the area does. Our guide on how much area a ton of gravel covers has the full chart.

Same caveat applies. These coverage figures ride on that 1.4 tons per yard average, so a heavier or lighter material shifts them. Confirm with the supplier.

Should you order extra gravel for compaction?

Yes. Order about 10% more than your calculation says. Two reasons.

First, compaction. Gravel arrives loose and full of air pockets. Once you run a plate compactor over it, or once a season of driving does the job for you, the volume shrinks. Compaction can reduce loose volume by up to about 20%. If you order the exact loose volume for a 4 inch finished depth, you may end up closer to 3 inches after it settles.

Second, reality. Some gravel ends up in the grass. Some fills a low spot you did not notice. Some gets tracked out on tires. Spreading is never perfectly even, and thin patches show up right where you do not want them.

• Add about 10% to your calculated volume for settling and spreading
• Compaction can shrink loose volume by up to roughly 20%
• Deep builds should be compacted layer by layer, not all at once
• Round up to the nearest half ton at the yard rather than shorting yourself

Running short is worse than having a bit left over. A second delivery usually costs a full trip charge for a small amount of material. Leftover gravel goes in the shed and patches potholes for years.

Gravel or mulch for garden beds?

Both get calculated the same way, and both get sold in confusing units, but they do different jobs.

Gravel is permanent. It does not break down, it does not need topping up every spring, and it holds a clean edge. It suits paths, drainage strips, xeriscape beds, and anywhere near a downspout. The trade-off: it heats up in the sun, it is a pain to remove once it works into soil, and it adds nothing to the dirt.

Mulch is temporary on purpose. It decomposes and feeds the soil, keeps roots cooler, and is far lighter to move. The cost is that you replace it every year or two. Around plants that you actually want to grow, mulch usually wins.

A practical middle ground we see a lot: gravel for the hardscape and drainage zones, mulch for the planted beds. Do not gravel a bed just because it looks tidy in a photo. Ask whether anything living needs that soil.

If you land on mulch, the volume math is the same formula but the units change, since mulch sells in bags and yards instead of tons. Start with how much mulch you need, then check how many bags of mulch are in a yard before you decide between bagged and bulk.

Bottom line

Cubic yards = area in square feet x (depth in inches / 12) / 27. Multiply cubic yards by about 1.4 for a working tonnage, confirm the real density with your supplier, then add roughly 10% for compaction and spreading. A 10x20 driveway at 4 inches lands at 2.47 cubic yards, about 3.5 tons. Measure the area, pick the depth from how it will be used, and let the Gravel Calculator handle the arithmetic. Then call your local yard for a price, because that part changes with your zip code.