Gallons R4 R6 0.5 (116) 9 4 1.0 (231) 17 8 1.5 (346) 25 12 2.0 (462) 34 15 3.0 (693) 50 23 Reservoir Capacity: R4-14cu.in. per inch of length. R6-31.6 cu.in. per inch of length. All Steel Construction Can Be Ordered In Any Length Mount Horizontally Or Vertically