Yes, but as Phil mentioned elsewhere I would not recommend this approach. The commercial preps are blended to a uniform consistancy so that there is no (or little) settling. If you make your own the particle sizes are all different so you run the risk of one component settling out. So you could, in theory, end up adding 37.5g pure sugar, pure salt or pure saltpetre to your kg of meat.
If you want to make a smaller batch of 100g say, then you can easily shake it up before taking your 37.5g out and minimise the riks of settling.
I prefer to make up for each individual use.
Dave