The problem with providing a simple answer that will apply universally to every scholarly thesis and dissertation is that each research project is unique and will therefore present its own specific requirements.
Several factors may play a role in determining the length of the final document.
A conceptual framework is very much like an accurate textual map of the territory investigated in your research, so it should allow you to include in meaningful ways everything you wish to report, discuss, interpret and argue.
• Outline the aims and objectives of your research.
You may also find it helpful to discuss the matter of introduction length with your supervisor or primary mentor, who will probably be able to give you more specific advice about the length of introduction expected for your particular research topic and approach.
Another excellent strategy is to consult successful theses and dissertations that have recently been completed in your department and discipline; their introductions, especially when the research is similar to your own, may serve as useful models of length.
Generally speaking, the more advanced the research, the longer the thesis or dissertation written to report it, so an undergraduate dissertation will be a lot shorter than a doctoral thesis researched in the same department and even one exploring the same research topic.
This does not mean, however, that undergraduate dissertations will always be of the same or a similar length, or that all doctoral theses will resemble each other in length.
There will usually be some sort of overall word or page limit set on the length of a thesis or dissertation, sometimes a lower limit that must be met as well as an upper limit that must not be exceeded.
Occasionally, there will also be information on how long each part of the document, such as the introduction, should be, but this is rare.