Mixing nutrients for a 5 gallon dwc???

I was playing with the nutrient calendar. Trying to see nutrients reccomendations for 5 gallon dwc. Then I realized I am not using 5 gallons of water. I should maybe calculate nutrients based on 4 gallons? I have the water filled just to the bottom of the net pot. I imagine I should measure it precisely, and calculate nutrients bases on the actual amount of water in the bucket when full?

Yup.

In my 5 gals buckets, 1" below the bottom of the 6" netpot is just over 3 gallons.. I scratched a line in the inside of the bucket at this point so i don't even measure ..i just fill to the known line.

I add my nutrients in proper ratios to one another, then dilute to my desired EC. Last, I pH the sauce to the desired value.

In your case, if do this in a container that doesn't have any plants in it, then transfer your nutrient solution into the DWC bucket when it's where you want it. If you make twice (or four or ten) as much as you need right away, you can store the rest and use it for topups.