Soil Underlay Volume Calculator
Ordering soil, underlay or garden mix is one of those jobs where guessing costs money — order too little and you are back at the landscape yard mid-project, order too much and you are paying to cart away the excess. This Soil and Underlay Volume Calculator works out how much material you need for raised beds, turf underlay, garden fill or top-up, in cubic metres or bags, so you can order once and get on with the job. It uses metric measurements and Australian supplier conventions, turning your bed dimensions and target depth into a clear volume. Enter your measurements below to get started.
Soil & Turf Underlay Volume Calculator
Work out how much screened soil or turf underlay you’ll need—and the trailer loads or delivered m³ cost—before you start your Aussie lawn project.
Formula: volume (m³) = area × depth(mm)/1000. Trailers = volume ÷ trailer vol.How this calculator works
The calculator multiplies the area you are filling by the depth of material you want, which gives the volume in cubic metres. It then converts that into the number of bags at a typical bag size, or the trailer loads and delivered cubic metres, so you can compare buying bagged product against a bulk delivery. Because a small change in depth makes a big difference to volume, the tool lets you set the exact depth for your job — a shallow top-dress needs far less than a deep raised bed. The result is a practical ordering estimate, not a precise soil-science figure.
Quick tip For irregular beds, split the area into simple rectangles, work out each one, and add them together. It is far more accurate than trying to guess an average for the whole shape.
What you need before using it
- The length and width of the bed or area, in metres.
- Your target depth of soil or underlay, in millimetres or centimetres.
- The bag size of your product, if you plan to buy bagged rather than bulk.
- Whether the area is a new raised bed, a fill, or a thin top-up layer.
Practical Australian guidance
Depth is where most projects go wrong. Many turf projects use roughly 100 to 150 mm of prepared base or soil improvement depending on the existing ground, turf type and supplier recommendation, so check what your turf grower and soil yard advise rather than assuming one figure fits every site. Raised vegetable beds usually want a good depth of quality mix for root room, while a simple top-dress over an existing lawn might only be 10 to 20 mm. Australian soil yards sell most bulk products by the cubic metre and often deliver by trailer or truck, so it can be cheaper to order in bulk once you pass a few bags worth. Soil and mixes also settle and compact over time, so allow a little extra.
Common mistakes to avoid
- Forgetting to convert depth from millimetres to metres, which throws the volume right out.
- Not allowing for settling and compaction, so the finished level ends up low.
- Mixing units — measuring the bed in metres but the depth in centimetres without converting.
- Buying lots of small bags when a bulk cubic-metre delivery would be cheaper.
Related calculators
Top-Dress Volume & Blend Calculator
Top-dressing soil or sand blend to level your lawn.
Lawn Size & Turf Quantity Calculator
Lawn area and turf rolls needed, with a waste allowance.
Frequently Asked Questions
Multiply the area you are filling by the depth you want to reach: area in square metres times depth in metres gives cubic metres. The calculator does this for you and also converts it into bags or bulk loads.
Many turf projects use roughly 100 to 150 mm of prepared base or soil improvement, but the right depth depends on your existing ground, the turf type and your supplier advice, so confirm before ordering.
It varies with bag size. As a rough guide, around 25 to 40 standard bags make up a cubic metre, so bulk delivery is usually cheaper once you need more than a handful of bags. The calculator uses your bag size for a closer figure.
Yes. Soil and organic mixes settle and compact over time, so adding a small allowance on top of the calculated volume helps the finished level stay where you want it.
Yes. Enter your measurements in metres and millimetres or centimetres. If you have imperial figures, convert them first, as one foot is about 0.3 metres.
Please note These volumes are planning estimates based on your measurements and typical Australian products. Actual needs vary with soil type, compaction, product density and site conditions, so treat the result as a starting point, allow a little extra for settling, and confirm depths and quantities with your supplier for larger jobs.
