MEASUREMENTS AND PURCHASE DECISIONS
Assign existing fill before adding bed layers.
How should existing fill affect a layered bed estimate?
Use the matching calculator
Use this decision sequence
- Use the measured internal base area.
- List planned layer depths from bottom to top.
- Assign existing fill to bottom layers first.
- Keep known solid displacement separate from the layer schedule and identify where it belongs before ordering each material.
Keep the quantities distinct
| Quantity or assumption | How to use it |
|---|---|
| Existing fill | Reduces new volume from the bottom upward. |
| New layers | Remain separate material lines. |
| Solid insert | Reduces total volume but needs a known layer assignment for per-material orders. |
Worked comparison
A 4 m² bed has two planned 0.20 m layers and an existing 0.10 m fill. New bottom-layer volume is 0.4 m³ and new top-layer volume is 0.8 m³. A known 0.1 m³ insert reduces the combined new volume from 1.2 to 1.1 m³.
Check before using the estimate
A combined displacement must not silently be deducted from every layer.
All dimensions, product properties, prices and specifications in this example are illustrative arithmetic inputs. Use the values from your measured plan, selected product data sheet and supplier quote. This guide does not choose construction specifications or certify safety.
Calculation and scope checked 2026-10-04. Methods and scope.