Price is per metre and it is sold by the metre. We recommend ordering a minimum boat length of chain to go with your new anchor.
If you can, go for 1.5 boat lengths.
It's the chain that does much of the work when anchoring.
It lays on the seabed and takes all of the snatch from the waves and other tidal influences. A longer length means less snatch on the anchor and less risk of the anchor pulling free.