By YardHatch · Published · Updated
Keep full precision while adding compatible quantities, then round once to the supplier’s selling unit. Round separate products separately; you cannot use excess sand to fill a shortage of topsoil.
Add only like quantities
Combine sections that use the same material, bag size and specification. Do not combine a compacted design volume with a loose delivered volume or add pounds to cubic feet. Normalize units and material states before summing.
A small example makes the difference
Suppose four small beds each need 2.2 cubic feet of one mulch. Rounding each bed to two 2 cubic foot bags produces eight bags. Combining 8.8 cubic feet first and dividing by 2 gives 4.4, so five bags cover the modeled total. The difference is three bags, not a change in the bed geometry.
| Method | Modeled need | Purchased 2 cu ft bags |
|---|---|---|
| Round each of 4 beds | 2.2 cu ft each | 8 total |
| Combine same product | 8.8 cu ft total | 5 total |
| Difference | Same modeled coverage | 3 bags |
Keep purchase increments explicit
Bulk material may be sold by whole or fractional yards. Ask the supplier for its increment and minimum. An order of 1.1 cubic yards rounded to a 0.5 yard increment becomes 1.5 yards; a 2 yard minimum changes it to 2.0. Both effects should be visible before comparing delivered cost.
Record leftovers without double counting
Whole packages can already provide extra volume. If a separate allowance is justified, apply it before package rounding and show both. Label leftovers as purchased surplus, not promised coverage: uneven depth, compaction and product variation can change actual use.
Make it your own estimate
These are modeled calculations. Actual products, installation conditions and supplier requirements control your order.
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Sources and method
University of Maryland Extension: Determining the area/size of a practice provides the relevant background guidance. Worked tables are YardHatch arithmetic using the visible assumptions, not source price data or field observations.