About Garden Sums

Who makes it

Garden Sums is made by Fernando Margareto, founder and editor. Fernando designs online tools that take a fiddly job and turn it into a few clear questions. He decides what each calculator does, how it works its answer out and what goes on the site.

It is worth being plain about what he is not. Fernando is not a landscaper, a builder or a surveyor, and he is not British. That is exactly why the site works the way it does: no figure on Garden Sums is a personal rule of thumb. Every density, depth, coverage rate and product size comes from published UK sources, and the calculators show you that figure so you can check it against your own supplier.

Why the site exists

Most garden jobs start with the same question: how much do I need to buy? Merchants' websites usually answer it for one product at a time, often in a unit you cannot order, and rarely explain how they got there. Generic calculators work in cubic yards or leave you to convert tonnes into bulk bags yourself.

Garden Sums tries to answer the whole question for a project. A patio is not just slabs: it is a type 1 sub-base, a mortar bed, cement, sharp sand and jointing compound. A fence is panels, posts of the right length, gravel boards, caps and post-fixing concrete. The calculators work all of that out together and give you one shopping list.

How the calculators work

Every calculator follows the same steps, and the worked example on each page prints them in full:

1. Area. You measure rectangles, circles, triangles or L-shapes, in metres or in feet and inches, and the areas are added together.
2. Volume or count. The area is multiplied by a depth (gravel, soil, bark), divided into strips (membrane, artificial grass), rows (decking) or panels (fencing), or multiplied by a rate (seed, paint, bulbs).
3. Weight, where things are sold by weight. Volumes are turned into tonnes with the material's density.
4. What you buy. The amount is rounded up to whole bulk bags, bags, rolls, boards, tins or packs in the sizes UK merchants sell, with an extra allowance you control.

The worked example under each calculator is produced by the same code that runs the calculator, so the explanation and the answer cannot drift apart. The formulas are covered by automated tests that compare them with sums worked out by hand.

Where the numbers come from

The figures come from UK manufacturers' technical data sheets and installation guides, from the product pages of UK builders' merchants and garden suppliers, and from RHS advice. Each value is recorded with its source and the date it was checked.

Sources often disagree a little. A tonne of topsoil, a litre of fence treatment or a sowing rate for lawn seed can vary between brands. When that happens, the calculator uses a typical figure, the page shows the published range, and you can type in your supplier's own figure instead. If a value could not be traced to a reliable source, it is not presented as one.

AI tools are used to help prepare and check the text and the code. The figures are not checked by a landscaper or an engineer: they rest on the published data above. That is why every result is an estimate, and why each page reminds you to confirm quantities with your supplier before you order. The disclaimer sets this out in full.

What the site does not do

Garden Sums does not give structural or safety advice. Depths for drives, shed bases, fence posts and decks are the usual published guidance for ordinary garden work, not a design for your site. Soft ground, slopes, drainage, heavy vehicles and anything attached to a building need a supplier's or a professional's view.

The site does not show prices either, because they change too quickly to keep right.

Your measurements stay with you

There is no account to create and no analytics. The calculators run in your browser, and the only things saved are your choice of metres or feet and your last calculation on each page, kept in your own browser so the Restore last calculation button works. The privacy notice and the cookies page explain the details.

Corrections and questions

If a figure does not match what your supplier tells you, or something on a page is unclear, please say so through the contact page. Each calculator shows the date its figures were last checked, and corrections are made as soon as they are confirmed.