Garden Bed Soil Volume Calculator

Enter your bed size and depth to see how much soil to order in cubic metres, litres, bags and trailer loads, and whether buying bulk or bagged is cheaper.

Filling a new garden bed is mostly a volume problem. Length times width times depth gives cubic metres, and everything you buy — bags of mix, a bulk delivery, a trailer load — is sold in some version of that number. Getting it wrong either way costs money: too little and you are back at the supplier next weekend, too much and you are left with a heap in the driveway.

Soil Volume Calculator

The prices below are example figures only — garden soil, bagged mix and delivery fees vary a lot between suppliers and regions. Replace them with your own quotes for a useful cost comparison.

Full guide, more detail, and a printable version at https://hollyshomestead.com.au/tools/garden-bed-soil-volume-calculator.html

Planning the bed itself? See our raised bed building guide, or work out what to cover it with using the Mulch Calculator.

How the Volume Is Worked Out

The sum is the bed’s footprint multiplied by its depth. A 3 m × 1.2 m bed is 3.6 m²; filled to 30 cm (0.3 m) it holds 3.6 × 0.3 = 1.08 m³, which is 1,080 litres. One cubic metre is exactly 1,000 litres, so you can move between the two without any conversion factor. For a round bed the footprint is π × (diameter ÷ 2)².

The calculator then adds a settling allowance. Freshly filled beds drop as air pockets collapse and organic matter breaks down, commonly by 10 to 20 per cent in the first season, especially with compost-rich mixes. Ordering the extra now means you can top up level with the rim rather than going back for a small second load.

If you fill the bottom of a deep bed with logs, branches and leaves — the idea behind hugelkultur-style beds — pick the share of the depth they will take. The soil figure drops and the coarse fill appears as its own line. Coarse material also shrinks as it rots, so keep that in mind when you plan the final soil level.

Bags, Bulk or Trailer Loads?

Bagged soil is convenient and fits in a car boot, but you pay for the packaging and handling: once a bed needs more than about half a cubic metre, bulk is usually far cheaper per litre. Bulk suppliers commonly sell by the cubic metre (some with a minimum of one), and delivery fees can swallow the saving on a small order, which is why the calculator rounds a bulk order up to the next half cubic metre and adds your delivery fee.

If you collect it yourself, check your trailer’s rated payload before you load. Damp soil weighs somewhere between 0.8 and 1.5 tonnes per cubic metre depending on the mix and how wet it is, so a trailer that looks half full can already be near its limit. The vehicle options above are cautious figures for soil; a heaped load of compost is much lighter than a load of clay loam.

Whichever way you buy, choose the mix to suit the bed: a free-draining raised-bed mix with plenty of compost for vegetables, or a plain garden soil for filling a deeper bed with a rich layer on top. For the long game, see our guide to building healthy soil, and use the Compost C:N Ratio Calculator to make some of the filling yourself.

How Deep Should the Bed Be?

As a rough guide, shallow-rooted crops such as lettuce, herbs and spring onions do fine in 15 to 20 cm. Most vegetables are happy with 25 to 30 cm, and deep-rooted crops like carrots, parsnips, tomatoes and potatoes are better with 30 cm or more. A raised bed built on top of loosened ground gets extra depth for free, because roots can keep going into the soil underneath, so the depth you fill does not have to equal the depth the plants can use. See the raised bed building and no-dig gardening guides for more on bed construction.