Cubic Feet - How do I separate from a larger bag?

Hi Gang!
First of all, Hi! I'm new here and look forward to contributing to the forum.

I have a quick question on making Mel's mix. I've found 4 cubic foot bags of vermiculite and have a bed that has a 71/2 cubic foot capacity.

This would mean I'm going to need 2.5 cubic feet of each component of the mix. I have the 4 cubic foot bag and need to get 2.5 cubic feet for the mix. Please confirm if my math makes sense below:

I'm seeing that a 5 gallon bucket is .67 cubic foot. This should mean 3x5 gallon buckets = 2 cubic ft.

Then, since 3.74026 = a half a cubic foot, I'm guessing I could do 3 and 3/4 gallons to measure the rest.

Does this logic makes sense? I really want to get this right as it seems like a huge part of the success of the garden.

If anybody has an easier method, I'm all gave for that as well.

I will be doing this all in a small VegTrug:
Small: 39 1/2” x 30” x 31 1/2” high overall; 7 1/2 cu.-ft. cap.

Some of your questions are answered in this 2 part video
https://www.youtube.com/watch?v=v0AroBDb7QA
https://www.youtube.com/watch?v=kzRfKzuOgZI

Gene

Here is another video that demonstrates the 'tarp' method of mixing that was mentioned in the other ... https://www.youtube.com/watch?v=sMNhRaI0Ppc