Substituting real ginger for ginger powder

[JarradsHopMachine]

Hey brewers. Sorry if i have posted this to the wrong thread firstly. I am going to try to do a ginger beer but want to use ginger powder instead of real ginger. The recipe i am going to use calls for 1.25kg of fresh blended ginger. Does anyone know how to convert this to powder? Also, has anyone used ginger powder in a brew before? I am looking at doing a 20+ litre batch hence the amount of ginger required.

 

[BrewZer]

Better Homes and Gardens suggests:
"If you don’t have any ground ginger, you can use fresh ginger; you’ll just need to use more because ground ginger is more concentrated. For every ¼ tsp. ground ginger, use 1 tsp. fresh grated ginger in recipes. This works in the opposite direction as well. If you don't have any fresh ginger you can substitute dried ground ginger using the same ratio."

If my math is correct, you'll need about 11 ounces of ground ginger powder.