Which calculator do I need?
| You want to… | Use | You get |
|---|---|---|
| Fill one or more raised beds or big pots, possibly with layers | Raised bed soil calculator | Litres per layer, bags, bagged vs bulk, shopping list, live 3D |
| Cover beds, paths or tree rings with mulch | Mulch calculator | m³, bags for every size, coverage per bag |
| Improve existing soil or start a new bed with compost | Compost calculator | m³ and bags for dig-in or top-dress depths |
| Balance a compost heap (greens and browns) | Compost C:N ratio calculator | C:N ratio, moisture and what to add |
| Lay a new lawn or bed at ground level, or level an area | Topsoil calculator | m³, tonnes, bags and trailer loads |
| Fill pots, planters or troughs | Potting mix calculator | Litres per pot (tapered, straight or square), bags |
| Order gravel, pebbles, crusher dust or road base | Gravel calculator | Tonnes, m³ and 20 kg bags with the right density |
| Level or feed a lawn | Lawn top dressing calculator | m³ and bags at 5–15 mm |
| Lay a new lawn from turf | Turf calculator | Rolls, underlay, cost and establishment water |
| Sow a new lawn or overseed a thin one | Grass seed calculator | Kilograms of seed by grass type, packs and cost |
| Feed a lawn or garden | Fertiliser calculator | Kilograms per feed and grams of N, P and K per m² |
| Mix a weed killer, liquid feed or seaweed tonic | Spray mix calculator | mL of product for your sprayer or can, from a rate per litre, a ratio or per m² |
| Turn a bulk quote into bags, or bags into m³ | Cubic metres to bags | Instant conversion for 25–70 L bags |
| Convert a price per tonne into cubic metres, or back | Cubic metres to tonnes | Tonnes, kilograms, trailer loads and coverage for 12 materials |
| Collect soil, gravel or mulch in your own trailer | Trailer load calculator | Safe load per trip and the number of trips |
| Build a raised bed from timber sleepers | Sleeper garden bed calculator | Sleepers to buy, cut list, posts and soil to fill it |
| Plant a bed, groundcover bank or hedge | Plant spacing calculator | Number of plants, plants per m² and cost |
| Know what to sow or plant this month | Planting calendar | Crops for your climate zone and month, with harvest timing and spacing |
| Size a rainwater tank for the garden | Rainwater tank calculator | Litres a year, rain to fill the tank, weeks of watering |
| Set sprinkler or drip run times | Watering calculator | Minutes per watering from a catch-can test or drip specs, litres a week |
| Lay an artificial lawn | Artificial grass calculator | Cheapest roll layout, joins, crushed rock, crusher dust, sand infill and pegs |
| Fix acid or alkaline soil | Soil pH calculator | Grams of lime, dolomite or sulfur per m², split into safe doses |
| Pave a patio, path or driveway | Paver calculator | Pavers with the joint counted, road base, bedding and jointing sand, dig depth |
| Lay a stepping stone path | Stepping stone calculator | Stones and gaps set to your stride, mortar bags, pebbles and weed mat |
| Edge a lawn or garden bed | Garden edging calculator | Steel lengths, plastic rolls, pine boards or bricks, with stakes and pegs |
| Build a garden retaining wall | Retaining wall calculator | Blocks or sleepers, posts, drainage gravel, ag pipe and the approval limit |
| Set fence, clothesline or letterbox posts | Post hole concrete calculator | Bags of concrete per post by brand yield, and gravel |
| Build a Colorbond or timber paling fence | Fence calculator | Panels, posts and footing depths, or posts, rails, palings and nails, with concrete |
| Pour a slab, path, footing, pier or steps | Concrete calculator | m³, bags by brand, the ready-mix order with short-load fee, mesh and bar chairs |
| Build a timber deck | Decking calculator | Lineal metres of boards, joists at the AS 1684 spacing, and screws |
How the calculators are built
Every calculator on GardenMaths follows the same principles:
- Metric first. Centimetres and millimetres in, litres and cubic metres out, tonnes where the product is sold by weight.
- Your prices, not ours. Example prices are clearly labelled and disappear as soon as you type your own. We do not sell products or take commissions from suppliers.
- Round up. Bag counts always round up to whole bags; volumes are shown to three decimals so nothing is hidden.
- Show the working. The formula and a worked example appear on every page so you can check the result by hand.
- Nothing leaves your browser. There are no accounts, and the calculations run locally on your device. The Share link on the raised bed planner encodes your project in the URL itself.
If a result looks wrong, or a bag size or product you use is missing, tell us – corrections are usually live within a few days.