Patio Base Calculator: How Much Gravel You Need

A patio base calculator works out the volume of crushed stone, gravel, or sand required for a patio foundation. You enter the patio length, width, and the depth of the base layer, and it returns the volume in cubic yards and cubic feet. This article explains the formula, gives a worked example, and covers the practical details of ordering and placing a patio base.

Formula

The calculator uses the standard volume formula for a rectangular prism:

Volume (ft³) = Length (ft) × Width (ft) × Depth (in) / 12

Volume (yd³) = Length (ft) × Width (ft) × Depth (in) / 324

Where:

• Length – the longest side of the patio in feet (ft)
• Width – the shorter side in feet (ft)
• Depth – the thickness of the base layer in inches (in)

The factor 12 converts inches to feet, and 324 converts cubic feet to cubic yards (since 1 yard = 3 feet, 3³ = 27, and 27 × 12 = 324).

Worked Example

Using the default values from the calculator: length = 40 ft, width = 25 ft, depth = 3 in.

1. Convert depth to feet: 3 in ÷ 12 = 0.25 ft
2. Calculate volume in cubic feet: 40 × 25 × 0.25 = 250 ft³
3. Convert to cubic yards: 250 ÷ 27 = 9.26 yd³

The calculator shows 9.26 yd³ and 250.0 ft³, matching the manual calculation.

Why the Base Depth Matters

The base layer is what keeps your patio level and prevents it from sinking or cracking over time. A typical patio base is 4 to 6 inches of compacted gravel, with a 1-inch layer of sand on top for setting pavers. For a light walkway, 3 inches of gravel may be enough, but for a patio that will hold a table, grill, or foot traffic, 4 to 6 inches is standard. The calculator lets you try different depths to see how the volume changes.

If you are using pavers, the base depth does not include the paver thickness. The paver itself sits on top of the sand, so the base is below the sand. For a concrete slab, the gravel base is usually 4 to 6 inches, and the concrete is poured on top.

How to Choose the Right Gravel

Not all gravel is the same. For a patio base, you want a crushed stone that compacts well. Common choices include:

• Crushed limestone – compacts tightly and is widely available
• Crushed granite – durable and attractive, but more expensive
• Pea gravel – round and smooth, but does not compact well; not recommended for a base

The gravel should be angular, not round, so the pieces lock together when compacted. A mix of sizes, from fine dust to 1-inch stones, gives the best compaction. This is often called “crusher run� or “ABC stone� (aggregate base course).

Ordering and Delivery Considerations

When you order gravel, it is usually sold by the cubic yard. The calculator gives you the theoretical volume, but you should order about 10% extra to account for compaction and settling. When gravel is compacted, it shrinks by roughly 10–15%, so the actual volume you need is a bit more than the loose volume.

For example, if the calculator says 9.26 yd³, you might order 10.2 yd³ (9.26 × 1.1). Most suppliers will deliver in whole or half yards, so round up to the nearest half yard. In this case, 10.5 yd³ would be a safe order.

If you are buying gravel in bags, each 0.5 cubic foot bag covers 0.5 ft³. To cover 250 ft³, you would need 500 bags, which is impractical for a large patio. For projects over a few square feet, bulk delivery is almost always cheaper and easier.

Common Mistakes and How to Avoid Them

One of the most common mistakes is mixing up units. Always measure length and width in feet, and depth in inches. If you measure the patio in meters, convert to feet first (1 m = 3.281 ft). The calculator assumes feet and inches, so using metric directly will give wrong results.

Another mistake is forgetting to account for compaction. If you order exactly the loose volume, you will run short after compacting. Always add 10% to the calculated volume.

Also, do not forget the sand layer. The calculator only computes the gravel base. For a paver patio, you need an additional 1 inch of sand over the gravel. That sand is not included in the base volume.

Limits of the Formula

This calculator assumes a flat, rectangular patio. If your patio is irregularly shaped, you can break it into rectangles and calculate each one separately, then add the volumes. For a circular patio, use the formula for a cylinder: π × radius² × depth. For a triangular area, use 0.5 × base × height × depth.

The formula also does not account for slopes. If your patio is on a slope, you may need more gravel on the low side to create a level surface. In that case, measure the depth at the deepest point and use that as your depth, or calculate the volume as a wedge.

Frequently Asked Questions

How deep should a patio base be?

For a standard paver patio, 4 to 6 inches of compacted gravel is typical. For a light walkway, 3 inches may suffice. For a patio that will support heavy furniture or vehicles, go with 6 inches or more. The calculator lets you try different depths to see the volume difference.

Can I use pea gravel for a patio base?

Pea gravel is round and does not lock together, so it shifts under weight. It is not recommended for a base layer. Use crushed stone with angular edges, like crusher run or limestone, which compacts into a firm surface.

How much extra gravel should I order?

Order about 10% more than the calculated volume to account for compaction and settling. When you compact gravel, it reduces in volume by roughly 10–15%. Adding 10% is a safe margin.

Do I need a sand layer on top of the gravel?

For paver patios, yes. A 1-inch layer of coarse sand over the compacted gravel provides a smooth bed for the pavers. The sand is not part of the base calculator; you need to add it separately.

Can I use the same calculator for a concrete slab base?

Yes, the volume calculation is the same. For a concrete slab, you still need a gravel base of 4 to 6 inches. The calculator gives you the gravel volume; the concrete volume is calculated separately using the slab thickness.

What if my patio is not a perfect rectangle?

Break the area into smaller rectangles, calculate each one with the calculator, and add the volumes. For a circle, use the formula π × radius² × depth. The calculator works for any rectangular section.

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in l | Lawn length | ft | 40 | 0 | 100000
in w | Lawn width | ft | 25 | 0 | 100000
in d | Depth | in | 3 | 0 | 120
out yd | Volume | yd³ | l * w * d / 324 | 2
out ft3 | Volume | ft³ | l * w * d / 12 | 1