Quick reference: the numbers gardeners look up most
The figures below are the ones that come up again and again in the guides. They are rounded for use in the aisle; the calculators give exact results for your own measurements.
| Question | Short answer | Details |
|---|---|---|
| Litres in a cubic metre | 1,000 L | Bags per m³ |
| 30 L bags in a cubic metre | 34 (33.3) | Converter |
| Raised bed depth for most vegetables | 30 cm | Depth guide |
| Raised bed depth on concrete or paving | 45–60 cm | Depth guide |
| Mulch depth (organic) | 50–75 mm | Mulch calculator |
| Compost to dig into an existing bed | 50 mm | Compost calculator |
| Lawn top dressing per application | 5–10 mm | Lawn calculator |
| Bulk soil becomes cheaper than bags at about | 0.5–1 m³ | Bagged vs bulk |
| Weight of a cubic metre of garden soil | 1.2–1.4 t | Weights |
| Gravel weight per loose cubic metre | ≈ 1.5 t | Gravel calculator |
| Settling allowance for fresh soil mixes | 10–15 % | Soil mix guide |
| Standard for garden soils / composts / potting mix | AS 4419 / AS 4454 / AS 3743 | Reading the label |
| Lime to raise pH by one unit (sand / loam) | ≈ 200 / 400 g/m² | Soil pH guide |
| Home kit vs lab (CaCl₂) pH reading | lab ≈ 0.5–0.8 lower | Why they differ |
| Bedding sand under pavers | 25–30 mm | Paving guide |
| Retaining wall without approval | 0.5–1.5 m by state | Approval guide |
| Timber fence post depth (1.8 m fence) | ≈ 600 mm | Post depth guide |
| Minimum pool fence height | 1.2 m (1.8 m on a boundary in NSW and SA) | Pool fence rules |
| Legal load in a 6×4 trailer (750 kg ATM) | ≈ 500 kg = 0.38 m³ of soil | Trailer calculator |
| Turf underlay under a new lawn | 100–150 mm | Topsoil calculator |
| Starting gypsum rate on dispersive clay | ≈ 200 g/m² | Clay soil guide |
| Clay to mix into a new bed on sand | 3–5 kg/m² | Sandy soil guide |
| Soil depth above a wicking bed reservoir | ≈ 300 mm | Wicking bed guide |
| Straw mulch richest in nitrogen | Lucerne | Straw mulch guide |
| Rain collected per m² of roof per mm of rain | 1 L (≈ 0.8 L after losses) | Rainwater calculator |
| Plants per m² at 30 cm, offset rows | 12.8 | Spacing calculator |
| Water per watering day (Perth, Darwin) | 10 mm = 10 L per m² | Watering calculator |
| Raised bed width reachable from both sides | 0.9–1.2 m | Bed sizes guide |
| Potting mix for one full-size tomato | 30–38 L | Pot size guide |
| Soil temperature to sow zucchini, pumpkins, cucumbers | at least 15–16 °C | Cucurbit guide |
| Nights before planting out tomatoes | above ≈ 7 °C, after the last frost | Tomato guide |
| Canberra years with a night of 2 °C or less after Melbourne Cup Day | 1 in 2 | The frost data |
| Standard turf roll in Australia | 1 m² (1,710 × 585 mm) | Turf calculator |
| Couch or kikuyu seed / ryegrass or fescue seed | ≈ 10 g/m² / 30–50 g/m² | Seed calculator |
| Most nitrogen in one lawn feed | ≈ 4.9 g N/m² | Lawn feeding guide |
| Ideal compost C:N ratio (by weight) | 25–30 : 1 | Compost ratio calculator |
| Soil temperature to germinate capsicum and chilli | at least ≈ 16 °C, best ≈ 29 °C | Capsicum and chilli guide |
| Soil temperature to plant sweet potato slips | above ≈ 20 °C | Sweet potato guide |
| Replace strawberry plants every | 3–4 years | Strawberry guide |
| Direct sun a soft-leaf buffalo lawn needs | ≈ 4 hours a day | Lawn grasses compared |
| Food compost worms eat a day | ≈ half their body weight | Worm farm guide |
| Minimum concrete for a path / a car driveway | 75 mm / 100 mm | Concrete calculator |
| 20 kg concrete bags in a cubic metre | ≈ 100–110 | Concrete calculator |
| Lettuce seed fails to germinate at | ≈ 29 °C (suffers above 25 °C) | Lettuce guide |
| Drippers apart in sand / loam / clay | 30 / 45 / 60 cm | Drip irrigation guide |
| Years before a vegetable family returns to a bed | 3–4 (5+ if possible) | Crop rotation guide |
| Marigolds suppress nematodes when | grown as a cover crop and dug in | Companion planting guide |
| First passionfruit crop | ≈ 18 months after planting | Passionfruit guide |
| Soil temperature to sow beans | ≥ 16 °C | Beans guide |
| Sweet corn ready after the silks appear | ≈ 20 days | Sweet corn guide |
| Heat that stops broccoli heading | ≈ 30 °C days, 25 °C nights | Broccoli guide |
| Spinach seed stops germinating above | ≈ 29 °C (silverbeet 35 °C) | Spinach and silverbeet guide |
| Soil pH for blueberries | 4.5–5.5 | Blueberry guide |
| Chicken manure nitrogen released in the first season | ≈ 40–60 % | Blood and bone vs manure |
| Maximum joist spacing, 19 mm hardwood / 22 mm pine decking | 500 / 450 mm | Decking calculator |
| Tonnes in a cubic metre of garden soil / gravel | ≈ 1.3 / 1.5 | m³ to tonnes |
How these guides are written
Each guide starts with a short direct answer, then explains the reasoning, shows the maths and lists the sources. Depths, densities and price ranges are compiled from Australian Standards (AS 4419, AS 4454, AS 3743), state horticulture and water-authority advice, and published supplier price lists, and are reviewed each season. Every guide shows the date it was last reviewed.
We do not accept sponsored content, and no product is recommended because a retailer paid for it. If something on a page is out of date or wrong, please let us know.