what size RESERVOIR for ebb and flow 8x4 tray

if i have 2 trays like that what size reservoirs do i need

how deep are they?

Here's what I came up with hope its correct. Just Blazed a blunt. Oh if one tray is for veg 1 for flower I would seperate the res's. This is also assuming a flood and drain setup but should be good for most any setup. 7.48 gallons per sq ft.
Water 6 inches deep: 8ftx4ftx.5ft= 16ft cubed=119.69 gal x2trays= 220 gal flood plus extra for the pump/s and between refills maybe
Water 3 inches deep: 8ftx4ftx.25ft= 8ft cubed=59.84 gal x2trays=120gal flood plus extra for the pump/s and between refills maybe
I changed this after I looked at it again. the math is right just seems like a lot of water. I can admit if I am wrong just thought I would take a go at it.

6 inches deep and they are for flowering ,can i put a single res. for both

and how big is 550 liters ok,thats about 180gallons