If you check the links under the Taxes board, you should find a post with links to a tax calculator. This should help you figure out your net income. After that, what you choose to spend it on will make a big difference in how far it goes.
My suggestion is to essentially put together your own 'market basket' of items for sake of comparison. Figure out what you spend money on here each week (groceries, entertainment, etc.), month (rent, utilities, phone, transport) and year (electronics, clothing, etc.). Then, check out various UK websites to see what the same/equivalent items cost. Gumtree.com is similar to Craigslist, so you can check there for rentals. All the major grocery stores (Tesco, ASDA, Waitrose) have websites, so you can check your food costs. Upmystreet.co.uk can help find tax & utility info for different areas.
It's a bit of homework, but you'll end up with a much more meaningful comparison than just asking 'what will x get me.'