l am after some new suspension forks but am concerned l am meausring in the wrong places, does 220mm sound like a right steerer length!? Can l buy longer or shorter forks than what l already have?
Cheers.

220 (about 8.5'') sounds pretty normal. You can always buy long and cut down or use spacers.

You measure the length from the seat of the crown bearing (where the steerer goes into the head tube) up to the top (tension) cap. Measured on the bike you will be within a couple mm because it is hard to get a strait and very accurate measurement.

l do not know where you want to buy it. If is in America or UK. You can get some idea. Go to http://actionsportsdepot.net/itenlist.cfn?category=90 I've see one of 265 mm
Http://shop.ebay.com one of 250 mm

The length of the steerer tube on a new fork is almost irrelevant because u will need to cut it to fit ur bike. What u need to worry about is the ''stack height'' of ur headtube on ur frame. You need measure the height of the headtube & the headset races & add to that whatever height u intend to use in spacers & then add the stack height of the stem u will be using & that gives u the length of steerer tube u need to fit ur bike. Nearly all new forks will have more than enough extra length unless you're buying an OEM or ''take-off'' fork that is already been cut to fit a bike.

For example, on my XC bike l have a large frame with a headtube & headset height of 154mm & then l need another 25mm between spacers & stem height so. l need at least 179mm steerer tube on a fork to fit my bike. l usually just round it to 180 & cut there. Anything longer is fine because l can cut it down to fit my frame.