Tank volume and dipstick chart

Volume is the tank’s inside measurements multiplied out, at 231 cubic inches to the US gallon. A rectangular tank fills in straight proportion to depth, and so does an upright round one (the circle’s area times the depth).

A round tank lying on its side does not. The liquid’s end face is a slice of a circle, so the first inches near the bottom hold little and the middle inches hold the most. The calculator works out that slice’s area at each depth and multiplies by the length, which is why a horizontal tank half way up the stick is half full but a quarter of the way up holds far less than a quarter. Domed or dished ends add volume the chart leaves out.

Weight is the volume times the weight of a sugar solution at that Brix, from the National Bureau of Standards table at 20 °C. Sap at 2 °Brix comes to about 8.4 pounds a gallon, the manual’s “slightly more than 8 1/3 pounds”, and a 40-gallon barrel of syrup to about 443 pounds against the manual’s 440. Hot liquid weighs a little less per gallon.

The North American Maple Syrup Producers Manual asks that tank framing be checked before a tank is filled, and again whenever its capacity or fill level goes up, since sap weighs about 8 1/3 pounds a gallon and concentrate more. The floor load here is the liquid alone spread over the tank’s footprint; it is a starting figure for that conversation, not a structural rating.