Multi aggregate banner image showing variation in sizes and colours of stones.

No one wants to get halfway through a job, only to discover that they’ve underestimated the amount of aggregate needed. Not only does it waste time, but it can also lead to higher costs as you miss out on savings from the original bulk purchase. Not to mention, it’s incredibly frustrating.

Use this guide to find out how to calculate the exact amounts of aggregate needed for a patio. Or head to Alsford Timber and see what our expert staff recommend.


Calculating aggregate

To find the amount of aggregate necessary for a patio is a relatively simple calculation. Multiply the width x length x depth, and this will provide you with an accurate measurement of the amount of aggregate required. In other words, calculate the area, and multiply by depth.

Calculating the area is done by multiplying the width by the length. For a patio with a width of 5 metres and a length of 3 metres, this would be 5 m x 3 m = 15 m².

This figure must then be multiplied by the depth. For a depth of 100 mm, the final calculation would be 15 m² x 0.1 m = 1.5 m3.

This calculation can be used no matter how small or large the space is. A patio with a width of 8 m, a length of 5 m, and a depth of 150 mm would be as simple as 8 x 5 x 0.15 = 6 m3.

For unusually shaped patios, you may need to divide the area up into sections and add the calculations together. For example, an L-shaped patio could be easily divided into two separate areas. Having calculated the amount of aggregate required for each separate area, it’s then a simple task of adding the two together, to find the overall amount needed.

Alternatively, round up the shape to a square, and calculate the overall amount. This will result in excess aggregate, but it’s always better to have too much, rather than too little.

Grey and shades of brown small stone aggregates arranges in diagonal bands.


Choosing depth

In order to correctly determine the amount of aggregate necessary for your build, it’s important to accurately determine the depth. This is the depth that will need to be excavated before you get to work on your patio.

For a patio, the average depth is usually around 150 mm, or roughly 6 inches. We wouldn’t recommend a depth any shallower than 100 mm.


How many bags of aggregate are needed?

Having calculated the amount of aggregate required, you’ll need to decide how much aggregate to actually buy. Aggregate is typically sold by weight, rather than metres squared. When you head to the builder's merchants to pick up your supplies, you need to understand the weight needed for aggregate.

You can browse our range of aggregates here.

While the calculation is simple, It can be difficult to accurately guess the amount of aggregate for a patio, as it will depend on the size of the aggregate itself. As a general rule, a 20-25 kg bag can be expected to cover around 0.5 m² at a depth of 50 mm.

For expert advice in choosing the right amount of aggregate for your patio, contact the experts at your nearest Alsford branch today.