Volume in litres = length (m) × width (m) × depth (m) × 1,000. A 2 m × 1 m bed filled 30 cm deep holds 600 L, which is 20 × 30 L bags of a single material or 0.6 m³ of bulk soil. With separate materials, round up the bags for each product: the sample's 100 L of gravel, 200 L of compost and 300 L of topsoil need 4 + 7 + 10 = 21 bags. Allow extra material for settling when choosing your fill depth.
The planner below does this for every bed and pot you add, keeps the layers within the bed's real depth, and compares the bagged total with a bulk delivery.
Your garden structures
Inside measurements, in centimetres
ExampleWe've loaded a sample 2 m × 1 m bed, 30 cm deep, with gravel, compost and topsoil layers to demonstrate separate bag counts. This is a volume example, not a soil recipe. For a bed on open soil, remove the gravel layer and choose your growing mix.
Your project totals
Bagged vs bulk delivery
Example prices – enter your supplier'sRough comparison: one bag price and one bulk rate are applied to every material, plus one delivery fee. Real products need separate quotes, and mixed loads or minimum orders may cost more. The bagged total is material only, without your own transport or fuel. A blank price is unknown, never free; enter 0 for a free item. Currency only changes the symbol – nothing is converted.
Your shopping list
| Material | Volume | Bags (approx.) | Or bulk |
|---|
Carries these litres per material into the project budget, where each supplier's own bag sizes, prices and delivery fee are used.
How the calculator works out your soil layers
You can calculate a single growing mix or several separate materials. The sample layers demonstrate the maths; they are not a recommended recipe for every bed. A bed on open soil does not need the sample gravel layer. See our raised bed soil mix guide to choose a suitable fill.
The planner treats the inside depth of the bed as a budget that the layers spend:
- It starts with the total inside depth you enter, for example 40 cm.
- Each layer you add (say 5 cm of gravel and 20 cm of compost) is subtracted from that depth, so you can always see how many centimetres are left to fill.
- If the layers add up to more than the bed's depth, totals pause and the bed is flagged until you adjust a number.
- Pots use the same rules with a round cross-section: π × radius² × depth.
bags per material = ⌈ material volume (L) ÷ bag size (L) ⌉
total bags = sum of bags for each material · 1 m³ = 1,000 L
Dimensions are stored in millimetres. The planner combines each material across all beds and pots, then rounds up its bag count, because you cannot buy 19.4 bags. Empty space is shown separately and excluded from volumes and costs until you add a layer to fill it.
Two raised beds, start to finish
Suppose you are building two raised beds, each 2 m long × 1 m wide × 30 cm deep, and your local landscape yard quotes a garden mix at $85 per cubic metre plus a $70 delivery fee, while 30 L bags cost $9 at the hardware store.
Bulk delivery wins by $188 even after paying for the truck. The break-even point with these prices is only about 0.33 m³ (11 bags): below that, bags are cheaper; above it, bulk pulls ahead quickly. Prices here are illustrative – type your own quotes into the planner to see your real break-even.
- Volume per bed
- 2 × 1 × 0.3 = 0.6 m³ = 600 L
- Total for 2 beds
- 1,200 L = 1.2 m³
- Using 30 L bags
- 1,200 ÷ 30 = 40 bags
- Bagged cost at $9/bag
- 40 × $9 = $360
- Bulk at $85/m³ + $70 delivery
- (1.2 × $85) + $70 = $172
Raised bed soil: frequently asked questions
How much soil do I need for a raised garden bed?
Multiply the inside length, width and depth in metres, then multiply by 1,000 to get litres. A 1.2 m × 0.9 m bed filled 40 cm deep needs 1.2 × 0.9 × 0.4 × 1,000 = 432 L, so 15 × 30 L bags or about 0.45 m³ of bulk mix. Add 10–15 % for settling if you are filling with a fresh, fluffy mix.
What size bags should I buy in Australia or New Zealand?
Garden soil, vegetable mix and compost are most often sold in 25 L, 30 L and 40 L bags at Bunnings, Mitre 10 and independent nurseries. Mulch usually comes in bigger 50 L to 70 L bags because it is light. Always compare the price per litre: a 40 L bag at $12 (30 c/L) beats a 25 L bag at $9 (36 c/L).
When is bulk delivery cheaper than bags?
Usually somewhere between 0.5 and 1 m³. Bulk soil costs a fraction of the bagged price per litre, but the delivery fee ($60–$120 in most metro areas) is fixed, so tiny jobs lose. Once you pass roughly 20–30 bags' worth, a delivery almost always wins – and you avoid carrying 20 kg bags. Our bagged vs bulk guide shows the break-even formula.
Do I need a gravel drainage layer at the bottom of a raised bed?
Not if the bed sits on open soil – water drains straight into the ground, and a gravel layer can actually hold water in the soil above it (a "perched water table"). A thin 3–5 cm drainage layer is worth it when the bed sits on concrete, paving or a sealed base, or when you are building a wicking bed. The planner lets you leave gravel out entirely.
What is the difference between garden soil, topsoil and potting mix?
Topsoil and "garden mix" are heavier, mineral-based products for beds and in-ground use. Potting mix is a lighter, composted-bark-based product designed to drain freely in containers; in Australia premium potting mix carries the black-tick mark of AS 3743. Never fill pots with garden soil – it compacts and drains poorly – and avoid filling a whole raised bed with potting mix, which slumps and dries out quickly.
Is my project saved? Do I need an account?
No account and no upload. Everything is calculated in your browser. Use the Share button to create a link that contains your beds, bag size, supplier prices and currency – open it on your phone at the hardware store, or print the shopping list.
Sources and method
- Standards Australia, AS 4419:2018 Soils for landscaping and garden use and AS 4454:2012 Composts, soil conditioners and mulches – the standards referenced when we describe "premium" garden mixes and compost. standards.org.au
- Standards Australia, AS 3743:2003 Potting mixes – source of the red-tick (regular) and black-tick (premium) potting mix marks.
- Bag sizes and typical price ranges are checked against the online catalogues of major Australian and New Zealand hardware chains and independent landscape suppliers; they change with season and region, which is why the planner uses your own prices.
- Volume formulas: rectangular prism (L × W × D) and cylinder (π r² × D). Cross-checked by hand against the worked examples on each page.
Written by DueRiva · Last reviewed 1 October 2026 · Report an error