How Much Soil Do I Need for a Garden Bed? A Simple Guide to Getting the Quantity Right

To work out how much soil you need for a garden bed, multiply the length, width and depth in metres. This gives you cubic metres. Add roughly 10% for settling. A typical 2m x 1m bed filled 30cm deep needs about 0.66 cubic metres of soil. Local soil conditions and whether you buy bagged or bulk will change the real-world answer.

Work out how much soil you need by multiplying length x width x depth. Measure all three in metres to get a volume in cubic metres. A standard raised bed measuring 2m long, 1m wide and 30cm (0.3m) deep needs 2 x 1 x 0.3, or 0.6 cubic metres. Most gardeners then add 10% for settling. That brings the real order closer to 0.66 cubic metres.

How to Calculate How Much Soil You Need for a Garden Bed

The formula is straightforward once the units are in metres. First, multiply the bed’s length by its width to get the area in square metres. Then multiply that figure by the depth of soil you want. The result is the volume in cubic metres. Suppliers across Sydney and the Southern Highlands measure and sell bulk soil this way.

Depth is where most people get the calculation wrong. Convert centimetres to metres before multiplying. Mixing units is the most common source of ordering mistakes. Fifteen centimetres becomes 0.15 metres. Thirty centimetres becomes 0.3 metres. Once everything’s in the same unit, the maths stays simple.

If you’d rather work in litres, multiply your cubic metre figure by 1,000. This matters because Australian suppliers almost always sell bagged soil by the litre. They quote bulk soil and trailer loads by the cubic metre instead.

A Worked Example for a Typical Garden Bed

Picture a garden bed 3m long, 1.2m wide, filled to a depth of 25cm. That’s 3 x 1.2 x 0.25, which equals 0.9 cubic metres. Add the usual 10% buffer for settling, and the real order comes to roughly 1 cubic metre.

For a smaller bed, say 1.5m by 1m at 20cm deep, the calculation is 1.5 x 1 x 0.2, or 0.3 cubic metres. That’s a manageable trailer load for most weekend gardeners. It also fits well within a single delivery run.

Soil does settle once it’s watered in. It can lose 10 to 15% of its volume within the first few weeks. Ordering exactly to the calculated figure often leaves a bed slightly short once everything beds down. That’s why the buffer matters more than it seems.

The same formula scales up easily for a full landscaping job. Picture a homeowner refreshing four garden beds, each 2m by 1.5m at 25cm deep. Provided the beds are roughly the same size, they can simply multiply one bed’s volume by four rather than measuring each bed separately. That comes to 0.75 cubic metres per bed, or 3 cubic metres across all four once you add the settling buffer. Builders and landscapers working across several properties in a week often use this shortcut. It lets them quote jobs quickly without re-measuring every site from scratch.

Topsoil, Garden Soil or Potting Mix? Choosing the Right Blend

The right product depends on what’s going into the bed, not just how much space needs filling. Plain topsoil is best for bulk filling, levelling and grading, where the goal is structure rather than nutrition. Garden soil combines topsoil with compost and organic matter. It suits vegetable patches and flower beds where plants need ongoing nutrition. Potting mix, meanwhile, is a lighter, free-draining option. Manufacturers formulate it specifically for containers and raised planters rather than in-ground beds.

Sustainable Gardening Australia, a not-for-profit body focused on soil health, highlights organic matter content as a key factor here. It shapes how well a garden bed holds moisture. It’s also key to how well a bed feeds plants over time. That’s exactly why plain topsoil alone often falls short for anything you actually want to grow well. Most established gardens do best with a topsoil-and-compost blend rather than either extreme on its own.

Why Sydney and Southern Highlands Gardens Often Need More Than the Formula Says

Local soil conditions change the real-world answer more than most calculators account for. Sydney basin soils are often clay-heavy. Clay compacts down noticeably once it’s wet. This is one of the most common reasons Wilton Sand & Soil customers come back for a top-up load a few weeks after their first delivery.

Southern Highlands properties, by contrast, often sit on sandier, more free-draining, sandstone-derived soil. This type of soil settles differently again. It can also mean a garden bed needs a slightly deeper fill to hold moisture through a dry Sydney summer. Neither condition is a problem. However, knowing which one applies to your block before you order saves a second delivery later.

As of 2026, most online calculators still don’t account for this kind of local soil variation. That’s because most calculator tools use a single generic formula rather than accounting for the ground conditions of any particular region.

Buying in Bulk or by the Bag — What Actually Works

Bagged soil suits small top-ups, potted plants, and beds under about a quarter of a cubic metre. Anything larger becomes expensive and awkward to carry bag by bag. Once a project passes that rough threshold, buying in bulk by the cubic metre almost always works out more practical.

Bulk orders also mean the soil arrives screened and consistent, load after load, rather than varying bag to bag. For a full garden bed rebuild or a new landscaping project, a bulk cubic-metre order removes most of the guesswork bagged soil involves. The truck delivers it straight to where you need it.

There’s also an access factor worth considering before deciding between the two. Bagged soil makes sense for a backyard with narrow side access, since you can carry bags through a gate a few at a time. A bulk load, however, needs somewhere for a truck to tip it. That might be a driveway, a nature strip, or another spot the truck can reach directly. Checking access before ordering in bulk avoids a delivery day surprise. It’s worth mentioning any tight access when placing the order.

Getting Your Soil Delivered Without the Guesswork

Once you’ve worked out the quantity, getting it to the right spot is the next hurdle. Wilton Sand & Soil delivers using its own tipper trucks rather than third-party freight. That means delivery dates stay in-house, and the driver places the load exactly where you need it rather than dumping it at the kerb.

Checking the delivery information page first helps confirm scheduling before the order goes in. This applies whether the job needs a single trailer load of garden soil or a full truckload of top soil. Smaller container or raised-planter jobs, meanwhile, often suit potting mix better than garden soil, since manufacturers formulate it specifically for confined spaces.

Ready to Order the Right Amount?

Getting the quantity right the first time saves a second delivery and keeps a project moving. Wilton Sand & Soil’s team has spent two decades helping Sydney and Southern Highlands homeowners, landscapers and builders work out exactly what a job needs. That might be a single bag or a full truckload. Get a quote today and order with confidence.