Results are estimates
The calculators work from the measurements you enter and from typical figures published by UK manufacturers, merchants and the RHS. Real materials vary: a bulk bag of gravel can weigh a few per cent more or less depending on moisture, topsoil settles by different amounts, paint covers rough wood far less well than smooth wood, and product sizes differ between brands. A small measuring mistake can also change the answer a lot.
Each calculator shows the figures it uses and lets you change them. If your supplier gives a density, a coverage rate or a pack size for the product you are buying, use theirs.
Check with your supplier before you order
Confirm quantities, sizes and delivery details with your supplier before you buy. Merchants know their own products, their bag weights and what they can deliver to your property.
Not structural or professional advice
Garden Sums does not give structural, engineering, building or safety advice. Depths and sizes for drives, shed bases, fence posts, decks, walls and ponds are the usual published guidance for ordinary garden work, shown only to help you estimate materials. They are not a design for your site.
Ground conditions, slopes, drainage, loads, frost, trees, services under the ground and nearby buildings can all change what is needed. For anything that has to carry weight or stay standing, ask your supplier, a qualified professional or your local authority's building control where it applies.
Safety
Lifting bulk bags, cutting slabs, mixing cement and digging post holes carry risks. Follow the manufacturers' instructions and safety data sheets, and use the right protective equipment.
Sources and changes
Figures are taken from UK sources and checked on the date shown on each page. Manufacturers change their products and their data, so a figure can go out of date. If you notice one that no longer matches, please say so through the contact page.
Liability
As set out in the terms of use, Garden Sums is not liable for losses caused by relying on a result, as far as the law allows.
Last updated 28 October 2026