Count shared rectangular coverage once.
Does summing measured zones count a shared portion more than once?
Use the matching calculator
Use this decision sequence
- Put all rectangles on the same measured coordinate system.
- Use width and height for each zone, not the endpoints as dimensions.
- Keep every zone that actually contributes to the covered union.
- Compare the combined area with the uncorrected sum before purchasing.
Keep the quantities distinct
| Quantity or assumption | How to use it |
|---|---|
| Summed areas | Counts shared regions repeatedly. |
| Union area | Keeps every covered position only once. |
| Triple overlap | Must be reconciled across all zones, not deducted separately for every pair. |
Worked comparison
Two 2 m by 2 m zones offset by 1 m in both directions each cover 4 m². Their shared square is 1 m², so the union is 7 m² rather than 8 m². Adding a third zone entirely inside either rectangle changes the area sum but leaves the union unchanged. Pairwise subtraction can fail when three zones overlap.
Check before using the estimate
Use axis-aligned rectangles and one coordinate origin. The result describes coverage, not property ownership or a boundary survey. The example values are illustrative arithmetic inputs. Replace them with your measured plan, selected product information and actual quote where relevant.
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.