Measure a component with linearly changing thickness.
When is average endpoint thickness a valid volume input?
Use the matching calculator
Use this decision sequence
- Measure the rectangular plan dimensions.
- Measure thickness at each end along the direction of the taper.
- Confirm the thickness changes linearly and is constant across each cross-section.
- Use the average of the two endpoint thicknesses, then add your volume allowance once.
Keep the quantities distinct
| Quantity or assumption | How to use it |
|---|---|
| Constant thickness | Use one measured thickness throughout. |
| Linear taper | Use the mean of the two endpoint thicknesses. |
| Irregular thickness | Measure multiple cross-sections rather than assuming one linear taper. |
Worked comparison
A 4 m by 3 m component changes linearly from 0.10 m to 0.20 m. Average thickness is 0.15 m and geometric volume is 1.8 m³. A 10% allowance gives 1.98 m³.
Check before using the estimate
The calculation measures supplied geometry; it does not select thickness or drainage requirements.
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.
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