How do I find out how many bytes or kilobytes are on a page

What you need is called a Bandwidth Monitor, it monitors the network traffic from and to your computer.

A free and open-source application called FreeMeter offers you this functionality for Windows. Take a look, there's a screenshot too:
http://sourceforge.net/projects/freemeter/

Thank you sssoooooooooo much for replying I will try this now xXx

You're welcome.  

As a general rule, video will be your biggest bandwidth user... then audio... with images next and finally just good old HTML code.

Does your current ISP have any sort of data caps?

I dont know, here is what i was thinking though, as a general rule (let me know if this sounds a good way of working it out) My google homepage on laptop is static - no adverts so no running data costs?

But sky sports changes pics etc about 12 times a minute so if average page is 600 bytes then 12 x 600 is 7200 so round it off (upwards to the 1000)
= 1 kilobyte

If I leave laptop on Sky Sports home page for 16 hours I will have used 1 MB


Or is that b*****ks

Regards
Gillian
xXx

A 600 byte image? Are you sure about that? If you are here's the math...

600 bytes per image X 12 per minute X 60 minutes per hour X 16 hours = ~ 7 megabytes.

How'd you come up with 1 megabyte in 16 hours?

as i said i am a newbie (/thickie) that why i am looking for help xXx