How many gallons of fuel oil does one inch equal in a 1000 gallon fuel tank?

Here is a tank chart that should help. Generally, the oil tank has a bit of "headroom" at the top, so, for example, a 275 gallon tank only holds about 256 gallons of useable fuel. Check with your local fuel company to determine the useable fuel volume your tank contains.

http://www.sippin.com/oil%20tank%20measure%20chart.htm