How we calculate

Sources

We base recommendations such as mulch depth, soil mixes and plant spacing on university extension services and other public horticulture institutions. Each calculator lists its sources under the result, with links, so you can read the original guidance.

Formulas on the page

Each calculator explains its formula in plain language with a worked example. The maths is simple geometry and unit conversion; we do not use hidden factors or adjustments.

Units and rounding

You can switch between imperial and metric units at any time. Internally every calculator works in metric units and converts at the edges, which avoids rounding errors from mixing feet and inches. We round quantities you buy, such as bags, up to the next whole unit. Volumes are shown to two decimal places.

Review

Our editorial team checks each calculator against its sources before publishing and again when guidance changes. The date of the last review is shown on every calculator page.

Limits

Results are estimates for planning and buying, not engineering, legal or safety advice. Local soil, climate and plant varieties vary, and your local extension office is the best source for advice specific to your area. For fences, local building codes, permit and setback rules and HOA rules come first, and buried utility lines must be marked (call 811) before anyone digs a post hole.

Corrections

If you find an error, email jonas@sport-calculator.com. We fix confirmed errors and update the review date.