It really does depend of the business model of the site. Most e-commerce setups would probably fit well comfortably inside 500Mb of webspace with a 100Gb traffic allowance.

A photostock site by contrast would need upwards say of 10Gb+ of storage and eat its way well towards 100Gb of traffic a month as the business model is akin to panning for gold. As you don't know what people want for that 'golden' pic so you have to carry a lot of rubble.

I mostly agree with Lovelogic. But I'd say for an e-commerce site, even 500mb is huge. 100mb is probably more than adequate. Bandwidth is where they get you though. If you're expecting a decent amount of traffic, you want quite a bit of bandwidth. Running out means more than just missing out on some sales, it will impact your SEO and credibility.

100GB/month is likely enough, but if you rank for a couple big keywords and you're serving large graphics to half a million people, you could eat that up pretty quick. It's unlikely though.

If you're concerned about it, try optimizing your site. Enable gzip if it isn't already. Reduce your image quality as much as possible before it becomes visible. Avoid pre-loading elements that visitors may or may not actually request. A few simple things like that and you can drastically reduce the amount of bandwidth that each visitor uses.

I agree also, however my aim of this post was to get an idea of the amounts of storage and traffic people are 'actually' using with their different sites as opposed to a general response.

I have a server with a bunch of free capacity atm and am considering offering a free hosting service for small website owners, or those new to the field wanting to play around with their sites live before considering paid options and am wondering how much restrictions I should put on the hosting account before they need to consider a paid service

I think the bandwidth of 500MB/month with diskspace of 50GB-100GB/month is adequate for traffics up to 30k/month.

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I'd give them like 10GB transfer and 1GB space, something in that range. People with established or popular sites probably won't consider free hosting anyway.

To avoid any mistake when choose space, you must be know, how many number of traffics do you have? This is very important for you if you have high traffics.

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Well I gave the ballpark figures of 500MB/100GB as these are the basic allowences for just two of the better free webhosting providers out there. As a couple of you pointed out this is quite generous and few sites are likely to bump up against these limits.

Visitor traffic is however a tougher nut to predict for any site, in fact I'd say it's imposible. Unique content or features certainly helps as does social networking by what few visitors who find you organically via the search engines but ultimately it takes TIME to achieve a decent footfall. Advertising campaigns can be useful for speeding things up but it's a bottomless pit money pit with no guarantee of results.

My own little job search project did not take off until I physically put up a handfull of A4 flyers near recruitment agencies in just one town. It went from under 100 visitors a day to 400/day in the space of week and is holding at that level so far.