How much water is in my brute?

[bdyslm]

Stealing picture from another member. I have a 20g brute. I filled it up to the top edge of the larger indentation under the handle on the side. Is that 15, 17, 18 gallons? 

 

How do I know so I can properly calculate how much salt to dump in.

 

I'm sure someone has figured this out before.

 

[xabo]

To get a "rough estimate" multiply the LxWxH and divide by 231.

[tds2264]

That is my picture of a brute container I sold. I filled up 5 gallon buckets of RODI water to various increments, noted it with sharpie on the inside.