Re: need to figure my gal size of gas tank
Here's a helpful example...
The volume of the rectangle would be 16*12*34 = 6528 cubic inches. 1 cubic inch = .004 gallons so 6528 cubic inches would be .004 * 6528 = 26.112 gallons.
So for your tank... 16*18*12= 3456 cu inches. .004*3456~ 13.8 gallons.
Also, assuming your motor is 50:1 fuel/oil. That's about 2.5 oz of oil to each gallon of gas.
Not sure what the rectangle calculation is all about, but the OP gave dimensions of 16x18x12 which is indeed 3456 cu. inches.
1 cu. in = .004 gallons may be close enough for government work, but a better conversion is 1 gallon = 231 cu. inches.
So 3456 cu. inches is closer to 15 gallons. (14.96 to 2 decimal places)
In practical terms, I doubt you would have a problem with either number.