How to convert 21 US dry barrels to US gallons?
We know (by definition) that:
We can set up a proportion to solve for the number of US gallons.
Now, we cross multiply to solve for our unknown :
Conversion in the opposite direction
The inverse of the conversion factor is that 1 US gallon is equal to 0.00155895691609977 times 21 US dry barrels.
It can also be expressed as: 21 US dry barrels is equal to US gallons.
An approximate numerical result would be: twenty-one US dry barrels is about six hundred and forty-one point four five US gallons, or alternatively, a US gallon is about zero times twenty-one US dry barrels.
 The precision is 15 significant digits (fourteen digits to the right of the decimal point).Results may contain small errors due to the use of floating point arithmetic.