There's no one definitive answer to this. As a very general rule, we suggest aiming to stay within three to four pages at the most. And if your board or senior team (or a company template, if you have one) suggests or dictates a length, always stay within that.
Do remember that โ unlike at school โ a word or page limit is not the same as a target to hit! The aim is to provide the necessary information and requested level of detail that allows the report to do its job. That may be to make sure the board is updated or able to make a decision based on the recommendations you make or research you present. If you can do that in a more succinct report, that's great. Don't feel you have to add more filler just to up the word count.