Quantities of materials used

Love the site. Very helpful. Just want to check my understanding so I am making the right comparisons. On your Origins Pocket 1500 you quote 300gsm of wool. This means on a King Size mattress (which I think is approx 3.4 sq m?) you are using 1000g of wool? Have I worked that out right?
I am thinking about getting the compact double for my son. Only found 1 manufacturer so far who has given me the weights of materials used but as an absolute value not gsm - just waiting for clarification on size of mattress quoted.
thanks