Rob
Separate geometric volume, loose material ordering, waste allowance and density-based weight without double-counting adjustments.
Four numbers, four different jobs
Garden material calculators become confusing when volume, weight and allowances are collapsed into one result. Bed & Barrow keeps the sequence visible so you can check what changed between the measured space and the order.
1. Geometric volume
This is the space described by your measurements: area multiplied by depth. It says nothing about material weight, settlement or the amount you may spill.
2. Loose-volume multiplier
If a project needs a compacted or settled in-place volume and you have a suitable supplied factor, multiply the geometric volume by it. Here the factor is loose volume divided by target in-place volume. A factor of 1 means no adjustment. It is not a percentage and no universal material factor is built in.
3. Waste or ordering buffer
The buffer is added once after the multiplier. A 10% buffer multiplies the loose requirement by 1.1. It is your chosen allowance, not a recommendation. If a supplier factor already includes the buffer, do not enter it again.
4. Bulk density
Density converts a compatible volume into mass. We ask for loose delivered bulk density because the adjusted order volume describes loose material. Particle density, compacted dry density and loose wet bulk density describe different things; do not swap them silently.
A checkable example
1 m³ target × 1.2 loose multiplier = 1.2 m³ loose
1.2 m³ × 1.1 waste factor = 1.32 m³ order
1.32 m³ × supplier loose density = estimated mass
The example factor and buffer are arbitrary inputs for explaining the arithmetic. They are not suggested values for your material.
Why “20% compaction” is ambiguous
If 20% of the loose volume is lost, the final volume is 80% of the original. To reach 1 m³ in place you need 1 ÷ 0.8 = 1.25 m³ loose. Adding 20% instead gives 1.2 m³. Ask which convention a supplier or specification means before translating it into the multiplier.
Ask the supplier these questions
- Is the stated density loose bulk density for the delivered product?
- What moisture and grading does it assume?
- Is the quoted yield per bag or per mass unit?
- Does an allowance already include compaction, waste or both?
No density or compaction ranges are prescribed here. Leave density blank for volume only and keep the multiplier at 1 unless a relevant source provides a factor.