Landscape material is sold by volume, while beds are measured by area. Depth connects the two and must use the same unit system before multiplication.
Convert depth before multiplying
Three inches is 0.25 feet; 75 mm is 0.075 metres. Multiply area by that converted depth to get cubic volume.
Reserved ad space
Account for settling and grade
Loose soil and mulch settle, while excavated beds may have uneven grade. Add a documented contingency rather than quietly changing measurements.
Volume is not weight
A cubic yard of dry mulch and a cubic yard of wet gravel have very different weights. Use supplier density and vehicle payload limits before hauling.
Reserved ad space
Practical takeaway
Measure area, choose installed depth, apply a visible contingency, and only then compare package or delivery sizes.
Planning note: Confirm product instructions, site conditions, safety requirements, and applicable local rules before purchasing or starting work.