What this site is
GardenMaths answers one family of questions: how much do I need, and should I buy it in bags or in bulk? The raised bed planner on the home page lets you build beds and pots layer by layer, watch them fill in live 3D, and get a shopping list with a bagged-versus-bulk comparison. Around it sit single-purpose calculators. They cover soil, mulch, compost and compost ratios, and potting mix. For lawns there are turf, grass seed, fertiliser, top dressing and artificial grass. For paths and structures there are gravel, pavers, stepping stones, edging, retaining walls, concrete, post holes, fences and decks. For water there are rainwater tanks and watering run times. There are also calculators for trailer loads, sleeper beds, plant spacing, soil pH, spray mixes and unit conversions. A planting calendar covers every Australian climate zone and New Zealand, and a set of guides explains the numbers behind them.
Everything is metric, everything is priced in AUD or NZD, and every calculator uses the bag sizes, depths and densities that Australian and New Zealand suppliers actually use. That local focus is the reason the site exists: most online garden calculators are American, work in cubic yards and 2-cubic-foot bags, and quietly assume a climate we do not have.
Who makes it
GardenMaths is a DueRiva project and is independently owned and operated. It is not affiliated with Bunnings, Mitre 10, any landscape supplier or any soil brand, and none of them has any say over what appears here.
How the numbers are checked
- Formulas are simple geometry (rectangular prism, cylinder, frustum) and are printed on each page with a worked example, so anyone can verify a result by hand.
- Depths, densities and standards are taken from Australian Standards (AS 4419 soils, AS 4454 composts and mulches, AS 3743 potting mixes), state horticulture and water-authority guidance, and landscape-industry references. Each guide lists its sources.
- Prices shown as examples are indicative ranges compiled from published retailer and supplier price lists. They are labelled as examples and vanish the moment you enter your own.
- Review dates appear at the bottom of every calculator and guide. When a bag size, standard or typical price changes, the page is updated and the date moved.
- Corrections are welcome and usually live within a few days – use the contact page.
How the site is funded
GardenMaths is currently free to use, with no accounts, subscriptions or paid tiers. Advertising and affiliate links are not currently active. If we introduce either, we will clearly label the relationship and update the privacy policy. Commercial relationships will not change calculator results or the assumptions shown in our guides.
Privacy in one paragraph
Your calculations run in your browser. New Share links keep the project after the # in the URL, which is not included in the normal request to our host. Anyone with the link can read the project; it is not encrypted. Older links put the project in a query parameter, which is sent to the host when opened. We still open those links and move the project into the # section in your browser. There is no database of saved projects. The full policy, including hosting and analytics, is at /privacy-policy/.
Technical notes
The site is plain HTML, CSS and JavaScript with no framework. The 3D bed viewer uses the open-source three.js library, loaded only after the page is ready so that the calculators work instantly on slow connections; if 3D is unavailable on a device, a 2D core sample takes its place. Pages are designed to work with keyboard navigation and screen readers, and to print a clean shopping list.
Last updated 1 October 2026