How to measure fuel tanks

I have a fuel gauge I install but I don’t trust it fully. I bought the truck with 2 150 tanks. Defiantly not original tanks for the truck from the looks of it 2006 century 14L. I have a 3 foot yard stick ruler. In inches what would be like a gallon or maybe even a quarter tank

 

With the yard stick Measure the diameter on the outside end of tank and divide that by 4. Then make those marks on the yard stick or a broom stick ( I use a fiberglass golf club handle that i cut the head off of and made marks on it). Each mark will represent a 1/4 tank. Dip into tank push to bottom and pull out to see were the wet mark ends. Check to see were the fuel gauge needle reads on gauge in dash and see how close it is. Pull sender from tank if need be and bend float rod to adjust.

 

Their really isn’t a inch equals so many gallons type rule. The middle will have more gallons to the inch. However you can measure how much fuel is in tanks. Then fill them remeasure. Divide gallons put in by the amount of inches put in. That will be your gallons per inch per say on what you have left.

 

Don't use a lighter to see how much is left,,

 

Tank Volume Calculator

 

Now that’s the absolute correct answer.
Good info

 

Dump a milk jug in. Mark the stick
Dump a milk jug in. Mark the stick
Dump a milk jug in. Mark the stick
You’ll get plenty of calcium if you buy new jugs

 

Stick

 

Just like @wore out posted on a round tank gallons per inch is hard to say because that last 1/4 will have much less fuel in it then the second 1/4 befween it and a 1/2 due to the shape of the tank. Rule of thumb on round tanks has always been once the gauge hits 1/4 it should be considered empty.

 

The calculator doesn’t take into account for this scenario. Round tanks with built in steps were fuel per inch will be more on the ends. So depth measurement with a stick is the only way to go to dial in a fuel sender.

That is a 90 gallon size tank but with step it is 75 usable gallons.