High yield cartridges have more room for toner. So, if you want to refill less often, you must at least buy one high yield cartridges and then refill it. An then, use it as long as it is usable.
Simon R ! I found this link answering a few Q's especially the document featured which they call as 5% coverage would give us a decent indication of the % coverage of a full a4 text page.
