There is no mandatory length of a thesis. Most well-written master’s theses have between 50 and 80 pages, Bachelor’s theses typically have between 40 and 60 pages. However, depending on your topic and your writing style, more or fewer pages may be appropriate.
Be aware that your thesis will only be evaluated based on the written document and the defense. If you did some nice work (that you might have shown to your adviser at some point) and forget to add it to your written document, it cannot be evaluated.