The outside length and width of a freestanding bath are not enough to set out a bathroom accurately. The base, waste cavity, rim, tap clearance, access points and manufacturing tolerances can all affect where the product actually sits.
The base may be smaller than the body
A sculpted bath can overhang its supporting base. The visible outline therefore does not identify where the load is transferred or where the waste needs to sit.
Use the current technical drawing
Check the base footprint, waste position, overflow, tap-hole options, service cavity, finished height and permitted installation method. Use the documentation for the exact model and finish.
Tolerances are normal
Hand-finished or composite products may have small variations. These should be allowed for in the floor, stone, wall and filler set-out rather than assuming every dimension is exact to the catalogue image.
Confirm the product before final work
Where the bath is central to the room, verify the delivered model before completing the final floor and surrounding joinery. A small difference in the base or waste can change the visual centreline.
Accuracy does not mean pretending the product has no tolerance. It means designing with the real product information and allowing the installer to work from verified conditions.
Read about why bath waste position affects the floor, or see why final measurement matters after finishes.