How Much Top Soil Do I Need? Calculate the Right Volume

Why It’s Important to Calculate Top Soil Correctly

Knowing how much top soil you need is key to planning any successful landscaping or gardening project. Whether you're laying turf, filling raised beds, levelling borders, or topping up depleted ground, having the right amount avoids delays, waste, and extra cost. Ordering too little soil can leave you short partway through, while ordering too much means extra expense and unwanted material to shift.

Top soil is usually measured in cubic metres or bulk bags, so a simple calculation based on your space’s dimensions will give you a solid estimate.

Measuring Your Space

To work out how much top soil you need, measure the length, width, and depth of the area in metres. Multiply these three figures together to calculate the volume in cubic metres. For example, a raised bed that’s 2 metres long, 1 metre wide, and 0.3 metres deep will need 0.6 cubic metres of top soil.

If you’re working in feet or inches, you’ll need to convert those figures to metres before calculating the volume. This helps ensure you’re matching the units used by suppliers, who usually list top soil in cubic metres or by the bulk bag. 

Understanding Bulk Bags and Volume

Top soil is often delivered in bulk bags, sometimes called tonne bags. Despite the name, a bulk bag doesn’t always contain a full tonne by weight. Instead, it typically holds between 0.7 and 0.9 cubic metres of soil, depending on the soil’s moisture content and density.

If your project requires 2 cubic metres of top soil, you’ll likely need at least 3 bulk bags to cover it comfortably. It’s always safer to round up slightly to allow for settling, compaction, and any unevenness in the space being filled.

Different Depths for Different Projects

The depth of top soil you need varies depending on what you’re planting. For lawns, a layer of 10 to 15 centimetres of top soil is usually enough. For flower beds or vegetable plots, 20 to 30 centimetres is better to support deeper roots. Raised beds and planters may require even more depth, depending on what’s being grown.

If you’re topping up an area rather than filling from scratch, remember to subtract the existing soil depth from your calculation to avoid overfilling.

Allowing for Compaction and Settlement

Top soil, especially when freshly delivered, is often loose and fluffy. Once it's spread and watered in, it will settle by around 10 to 15 percent. For this reason, it's sensible to overestimate slightly and mound the soil a little higher than your final required level. After a few weeks, the soil will naturally compress and form a more solid base for planting.

Keep this in mind when calculating volume — especially if you're filling large planters, building up borders, or preparing new beds for turf.

Tips for Ordering and Delivery

When ordering top soil, check what type you're buying — screened top soil, enriched compost blends, or loamy mixes each suit different purposes. For turfing, go for fine, well-draining top soil. For beds and borders, a richer mix with organic matter may be better.

Also consider access for delivery, especially if you're ordering in bulk. Make sure there’s space for a grab lorry or tipper truck, or choose bagged top soil if the site is harder to reach. Plan to use the soil shortly after delivery — leaving it exposed to rain or wind can degrade its quality.

Top Soil Shrinks More Than You Think

A common mistake is underestimating how much top soil settles after spreading. Once it’s compacted by watering, foot traffic, or the weight of plants, top soil can shrink by as much as 15–20% in volume, especially if it's loose or high in organic matter. This is more noticeable in deep beds or freshly tilled ground. If you’re filling an area that needs a firm finish — like under turf or around paving — it’s smart to add a little extra to account for this compression.

Levelling Uneven Ground Takes More Soil

When you’re levelling dips or raising low areas in a garden, it’s easy to underestimate how much top soil is required. Uneven ground takes more soil than flat areas of the same surface size because the soil must fill vertical space, not just spread across the surface. Even small depressions, once filled and compacted, can consume more volume than expected. If your lawn has significant hollows or you're building up a slope, calculate volume in layers and be generous with your estimate.

Blending with Existing Soil

If you’re adding top soil over existing ground, particularly in borders or beds, you may want to blend it into the existing layer rather than simply topping up. This promotes root integration and avoids layering, which can cause drainage issues. In this case, a slightly thinner layer of top soil may suffice, since you're mixing rather than building a standalone base — but be aware that tilling or blending soil also affects volume. Once mixed, the total depth may compress, so again, plan for a bit more than your surface calculation suggests.

Bag vs Loose: Impacts on Volume and Handling

Top soil in bulk bags and loose loads behaves differently. Bagged soil tends to be looser, with more air trapped inside — which means it appears more voluminous than it really is. Once spread and compacted, you might get less coverage than expected. Loose top soil from a tipper lorry is often denser and more compressed, so it spreads more evenly but is heavier to move.

If you're comparing prices or quotes, always convert into cubic metres, not tonnes, since weight can vary significantly with moisture content.

Soil Type Affects How Much You Need

The type of top soil you’re using also influences how much you’ll need. Light sandy soils settle faster and may need to be applied more deeply to retain moisture. Dense clay soils might need less volume but more amendment with organic matter to improve structure. For planting fruit or vegetables, you may want to use enriched or compost-heavy top soil — which, while more nutrient-rich, is also more prone to settling and leaching, especially after heavy rain.

Choosing the right type from the start can reduce how much you need in the long run by supporting stronger, deeper roots.

Use Tools or Calculators for Accuracy

If you're managing a large area or have multiple zones with different depths, it helps to use a soil volume calculator. Many UK suppliers offer online tools where you enter your measurements and get an instant estimate in cubic metres or bulk bags. This helps reduce guesswork — especially useful when working on terraces, raised planters, or split-level gardens.

Final Word

Working out how much top soil you need doesn’t have to be complicated. With a simple measurement and volume calculation, you can order the right amount for your space and avoid unnecessary waste. Whether you’re creating new beds, refreshing tired ground, or preparing for turf, accurate planning ensures your project runs smoothly — and that your plants have the best possible start.