Products that are purchased in loose random format and crazy paving are sold as a "cover metre" and grout joints have been allowed within the measurement.
When measuring up the required amount of stone wall cladding for your project, how you want the final product to look (grouted vs non-grouted) will depend on the final wastage quantity required.
SD&CO recommends allowing 15-20% wastage for tight (non-grouted) installations and 5-10% for grouted installations (~10-15mm thickness of grout lines). This is not an exact measurement, but will provide you with as close as possible quantities. You may still have a little bit of product left over, or you may be a little bit short. Each project will be different and you can only truly gauge how much is required by starting to install your stone cladding or crazy paving for your project.
1 Cover Metre