For business purpose, if anyone wants to purchase a new web hosting account, the user will definitely need storage space according to his requirements. Many factors are required to plan it accordingly. Most of the hosts are offering Unlimited Hosting space, some prefer to pay for a fixed plan. These may be cheaper and also provides more server resources per plan.
Emails
A maximum part of any web hosting account would be taken by email services. Anyone needs to determine that where and how will emails be stored and how long user will retain them on a server. He also needs to determine between intervals of mail download, a number of emails expected per day. This means if anybody doesn't download mails in a night then those emails will take how much space on a server. This is critical to ensure continuous web hosting services so that account would not get full.
Website
Storage space needed for a website is dependent on nature of the website. If a CMS based website or blog have updation on regular basis, then a user will need more space. In case of a static website made in HTML, a user will be able to measure space amount taken over a long period of time. To run website it is the best method to do a test with small pilot site contain layout and designs before going to the full-fledged website.
Storage of files
Many people want to install storage of file and apps retrieval on their account of web hosting. Apps are helpful to manage for file storage using same hosting space. If anyone plans to do that and web host allows storage space then a user will need to plan according to this additional space. If multi-user access to file storage is allowed then the user need to setup quotas or amount of space consumed by a user is restricted else space would be unmonitored for an instant.
Visitor's Files
If anybody allows uploading files from visitors or attachments will be submitted with their forms, then for storage space counting user may need to consider this factor. A Client has provided facility to his visitors to upload screenshots of their PCs with their website form. After that, a one-day entire hosting account of him was jammed as visitor uploaded attachment of 100MB on his account. Email and other services are blocked by it in which 80% storage space will be consumed. To protect this, a client has right to restrict file types and sizes for visitors to prevent extra usage of space. It is better that visitors would not be allowed to upload attachments in their forms, especially in comment forms which will direct to advertising and spam.
Databases
MySQL database is very popular and it contains usually fewer data and causes limitation of disk space, this can also be avoided in reference to space calculation. If any website is of CMS based used to store content and pages of a website then proper space estimation is required for a definite amount of space according to it.