Estimate hosting needs
Estimating hosting needs
How to estimate your hosting needs
I write this article especially for people who are new to web hosting. This is why I will only talk about the basic needs (in a shared hosting environment): space, bandwidth. Most of the people looking for advanced features (scripting, databases) already know what they want/need anyway.
So let's start with the space. Web space (disk space) is the amount of data you can store on the hard disk of the web server. Each web hosting account comes with a certain amount of space, usually over 50 MB. In recent times 1000 MB+ of space is a very common offer.
Obviously, the amount of needed space depends on the size of the website. Most websites are composed of html (text) pages with a few images (gifs or jpegs) or even a little bit of Flash animation. Text is very economical; it occupies very little space. Images and flash are more "expensive"; they require considerably more space. If you're new to the web you might think it's great to have a lot of colorful images to make your website really beautiful. Don't make this common mistake.
Your aim should be to say as much as you can on a page while maintaining it's size preferably under 50-60 KB including the images. The reason? There are still lots of people using slow dial-up connections of under 56 kbps. For them a 150 KB page will take more than 21 seconds to load (in ideal conditions, which are never met in real life). A 60 KB page will take more than 8 seconds to load. That's still a lot of time! A very good page size is under 30 KB.
Considering an average page size of 30 KB, you can put approximately 33 pages
on 1Mb of space. If you have 10 MB of space available, you could host 330 pages.
I only wish I had so many pages to put online, but don't worry, I'm working
on it! 
The idea is this: unless you run a busy forum or some other type of site where multiple individuals add content to the site, or you have a downloads type of site (for images, software, cartoons, etc) your needs for space are likely to be rather modest. Just keep in mind to achieve an average of 30KB/page and you should be more than fine even with 10 MB of web space.
The emails you receive are also occupying space and count against your quota. To make matters more difficult, you have to set a space allowance for each email address you add to your hosting account. If you have say a total of 10MB of space for your hosting account, and you set 5 MB for an email address, you'll only have 5 MB to use for your website's files. Luckily hosting accounts come with a lot of space these days.
Bandwidth is the amount of data that you're allowed to transfer per month (or at least that's the meaning of the word as it is used by most hosts on their sites). It includes all uploads and downloads regardless of the protocol used (HTTP, FTP, POP etc.). Bandwidth depends very much on the average page size, but it also depends on the number of visitors your website will have and the average number of pages they visit. For an average page size of 30 KB, 20,000 visitors per month and 3 pages per visitor your website will need about 1800 MB (1.8 GB) of bandwidth per month. Most hosting packages include significantly more bandwidth than that. Not to mention that 20,000 visitors per month is only a dream for most websites. Most don't even have 1,000 visitors per month.
I took you through all those numbers just to give you an idea how to estimate your needs. If you're just launching your website, chnaces are that you will not need neither a huge amount of space, neither a huge amount of bandwidth. For the vast majority of websites, some 10MB of space and 1Gb of bandwidth are more than enough.
Conclusion
Unless you have reasons to believe that your website will definitely have lots of visitors or otherwise use a lot of resources, I see little reason for you to worry about space and bandwidth.
Just make your own calculations and also try to make sure that the host you choose allows account upgrades. That is to make sure you will be able to get more space and/or bandwidth if/when you need it without going through all the trouble of changing hosts.
The end. Cheers!