That depends on the type material you are referring to. Also, these are two different types of measurements. Gallons is a measure of volume but the other is weight or mass. Please edit your question to include more context or details.
400lbs
250 LBS plus the weight of the tank
Depends on the manufacturer and specification standard of the tank, but roughly speaking at this capacity, there is about 2 pounds of steel for each gallon of capacity, so vacuum purged, the tank would weight approximately 400 lb. If it is filled with propane, each gallon of propane is 4.2 pounds at 60 degrees. Tanks are generally not filled beyond 80%, so maximum fill would be 672 pounds. Thus, full tank should be approximately 1000 pounds +/-.
Ford F-250 With One Tank (side) 18 Gal US, w/ Dual Tank (Side & Rear) 18+13 = 31 Gal
That depends how many mpg your vehicle does: My company car does about 4.15 mpg (it weighs 23 Tonne fully laden with 71 passengers and their luggage and has a 12 litre engine), so the tank to do 250 miles would contain: 250 miles ÷ 4.15 mpg = 6020/83 gal which would cost: 6020/83 gal x 4.15 per gal = 250. (Now you know why coach/bus hire is so expensive.) My personal car does about 50 mpg (on nice clear roads, like the autoroutes in France) which means my car's tank to do 250 miles would contain: 250 miles ÷ 50 mpg = 5 gal which would cost: 5 gal x 4.15 per gal = 20.75
The gas tank on the 2014 Lexus IS-250 holds 17.4 gal..
The gas tank on the 2006 Lexus IS-250 holds 17.1 gal..
The gas tank on the 2012 Lexus IS-250 holds 17.2 gal..
The gas tank on the 2013 Lexus IS-250 holds 17.1 gal..
The gas tank on the 2007 Lexus IS-250 holds 17.1 gal..
The gas tank on the 2011 Lexus IS-250 holds 17.1 gal..
The gas tank on the 2009 Lexus IS-250 holds 17.1 gal..
The gas tank on the 2008 Lexus IS-250 holds 17.1 gal..