How We Verify Our Calculators
A garden calculator is only as good as the figures behind it. A wrong seed rate, spacing or compost volume wastes money and a growing season, so we hold every number on this site to one rule: trace it to a real source, never guess. This page explains how we check our calculators and what we do when something is wrong.
The process
- ✓Every figure is traced to a named source before it goes live: RHS growing guidance, Met Office rainfall and frost data, gov.uk and Defra guidance, British Standards such as BS 3882 for topsoil and BS EN 16941 for rainwater harvesting, or a supplier’s published technical data.
- ✓Where a figure comes from a supplier, we name them on the page. Our topsoil and mulch calculators cite Rolawn’s coverage data, and our block paving calculator uses Marshalls’ laying specifications.
- ✓Every calculator has a pinned test: a fixed set of inputs with the expected result worked out by hand from the source, run automatically in desktop and mobile browsers before each release.
- ✓When we find an error, we correct the figure against the original source, re-run the affected tests, and redeploy. A known-wrong number does not stay live.
Verified, not guaranteed
Our calculators give estimates to plan and order from, not professional advice. Growing conditions vary by soil, aspect and season, so treat spacing, sowing and watering figures as starting points, and confirm material quantities with your supplier before ordering. For lawn feed, lime and other soil treatments, the rate on the product label takes precedence over our figures. For boundary disputes, retaining walls over a metre, or anything structural, speak to your local planning authority or a structural engineer.
Spotted an error?
Every calculator page has feedback buttons. If a figure looks wrong, tell us what you entered and what you expected: we investigate against the original source, fix anything that fails the check, and re-verify before the correction goes live. When a report shows a genuine error, the fix lands on the affected page itself, with a dated correction note where it matters.