Its important to calculate how many storage you need for your next web hosting plan. And sign up to a small hosting space or get into the wrong hosting package will caused lots of problem in short coming future.
Commonly, a web hosting company will offer you one or two web hosting plan to choose from. And usually you will start with the most basic plan, just to try out the new host, and take the smallest risk on your money.
If you sign up a hosting plan cause of good price, and not considering the disc space you require, then this will be the biggest mistake you can ever make. Initially, you will be thinking 1000MB will be sufficient for the coming one year or more. You havent calculate in disc space taken by your database, or media files, photos and pictures, webpage content and files uploaded by users etc. The website will keep growing and you will not have time to go through each files and do housekeeping each month. This will killing you, and wasted lots of time.
Do a simple calculation, how many webpage you will have. And allocate each page with 200kb of file size. That is more than enough. Then how many media files you going to have. If its video files, you will need to make the calculation carefully, and take into account the future growth rate.
After you had estimated the 12 months usage that you need, double it up. For example, you will require 10GB storage space for your website to run for the following 12 months, get a web hosting with 20GB storage space. You will need to reserve the space for yourself.
Usually you will be thinking, I will upgrade to 20GB when I need it. And usually web hosting company will screen through your files. And if they found many unused files for your website, they will write to you ask for clean up. You just triggered the big boss.
And even they proceed with space upgrade, its depend on the current server have remaining space or not. Note that most web hosting server is already 80% in used. Most the web spaces already in used by other account, and when you want to have more space, they might need to move you to the other server that have extra space for you. That will be subject to few hours of downtime. And you need to consider this as well.
Conclusion is that, buy more space even you not require them now. Commonly I will find web hosting that offering me 50GB storage space and above.