Erics,
The spread is the difference between the bid and ask price. This varies constantly as buyers and sellers change their quotes on a continual basis. It will also change depending on which platform you look at.
For instance, if you look at a direct access broker, then you get the true spread eg ABC company is being quoted at 12.45 / 12.47, this is a 2 tick (/ cent / pence / euro or whatever) spread, but at the exact time, a Spreadbet company my be offering ABC company at 12.42 / 12.49 as they make money on the spread rather than on commission charges.
So, how do you find out the spread - look at the price being quoted.