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 for mulch, compost and compost ratios, topsoil, turf, grass seed, fertiliser, potting mix, gravel, lawn top dressing, trailer loads, sleeper beds, plant spacing, rainwater tanks and unit conversion, and a set of guides that explain 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 free to use and has no accounts, subscriptions or paid tiers. It is supported by advertising, which is clearly separated from content and never influences which products or methods the guides recommend. We do not sell soil, mulch or anything else, and we do not earn commissions from the suppliers mentioned on the site. Details of the advertising and analytics services used are in the privacy policy.
Privacy in one paragraph
Your bed dimensions and prices are calculated in your browser and are not sent to us. The Share feature encodes your project into the link itself – there is no database of projects. The only thing stored on your device is your light/dark theme preference. The full policy 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 23 September 2026