EC011609 Bath -> EF000880 Volume: Total water capacity or usable water capacity?

Any preferences on how to use EF000880 Volume for things like EC011609?
Is this feaure referring to the total water capacity or to the usable water capacity?
Thanks very much in advance!

Again a very good question! Without any reference to a standard that says how deep the bath should be filled, which also depends on the size of the person sitting in the bath, this feature could only refer to the total volume of the bath? But is that information really useful, since no one will fill the bath to the edge. I see in the 2BA database that many products (85%) don't list the volume, probably to avoid confusion? But again, if there is no normed reference, only the total volume makes sense.