Why do you need it 4 or 5? Is this a seo job?
There is no exact number. The quality of your back links really counts and these is only determined by Google.
Work until you reach pr 4 or 5

Create high pr links and submit article it will help you.

there is no as such formalae for it. the more inner links are, are better, but PR is not increased by only having backlinks. there are other ways too

I agree with 'silveraden' he is right, no one really knows how google rank your site. I have experience with 2 sites. Both sites PR is same '3'. one of the sites have 1000 of backlinks, above 500 content page and monthly above 10000 visitors. On the other hand other site PR is same '3' monthly visitors only 100, baklinks 100 and more than 100 content page. So, how can you judge PR?:) so it is difficult to find how Google give PR to a site. So, it would be better if you keep all the aspects of SEO in mind, it will natuarally gain PR from google.

take care all the on-page SEO factor like
1.HTML & CSS coding should be clean.
2.Proper site navigation.
3.Proper Meta detail
4.'alt' tag on the image code
5.301 redirect
4.404 error page create
5.Internal link building
6.add social share button etc.......
7.update your site content weekly or daily

To get the PR you just have quality content, because backlink could only be counted if the content is relevant. And the quality of backlink is essential to increase PR, and please create them naturally.

Make quality backlinks........... hope so you see your update page rank...

Don't go for quantity dear. Just go for quality..You get quick results.

Be a part of the DaniWeb community

We're a friendly, industry-focused community of 1.21 million developers, IT pros, digital marketers, and technology enthusiasts learning and sharing knowledge.