Is there any rough rule of thumb how many hours of HD and SD programs are able to be watched per GB of bandwidth?

I know they recommend a 1 megabit/second internet connection for their lowest quality setting, so assuming it actually uses 1 megabit/second, that'll be 8192 seconds (about 2 and a quarter hours) of footage on the lowest quality setting for 1 gigabyte of bandwidth (8 megabits in a megabyte, and assuming your ISP takes 1024 megabytes in a gigabyte, rather than 1000)

Thank you.

Much easier would be to look at download option and it will tell you the size of the file.

If you look at the "Download Options" for an SD TV programme on iPlayer, you'll find that the file sizes amount to about 600-650 Mb per hour. I have assumed that the data rate for "Normal Bandwidth" SD streaming is about the same, and I seem to remember seeing roughly the same figure given by BBC staff on their Freesat iPlayer blog, which seems to confirm my assumption.

Actually, the equivalent figure for Freesat iPlayer was for the "Higher quality" stream, but this seems to correspond to the "Normal Bandwidth" stream on the iPlayer web site. The two streams are referred to as "Normal bandwith" and "Lower bandwith" on the web site, but confusingly on Freesat the lower one is given as the default option and the higher one described as "Higher quality". Anyway, I consider the higher of the two to be the norm in both cases, as the lower one (at about half the data rate I gave) is unacceptable quality to me.

Don't confuse the "Higher quality" option on Freesat iPlayer with HD (as I intially did). The file size for downloadable HD files is about 1.1-1.2 Gb per hour.

So the short answer to your question (if I'm not mistaken) is about 1.1-1.2 Gb/hr for HD, 600-650 Mb/hr for the better quality SD, and about half the latter for poor quality SD.

And more thank-yous.

I have yet to install IPlayer or its cousins and was concerned how it would fit with my broadband usage allowance.