You can't answer this question unless you know the dimensions of said barrel and the density of whatever liquid you want to measure the liters of.
1 liter equals 1 liter.
1 liter equals 1000mL
I liter equals about 4 cups. I liter equals about 4 cups.
1 liter equals 1000 milliliters
1 Deca liter
1 liter
200 teaspoons equals one liter.
1 liter = 1,000 milliliters
1 liter = 10 deciliters (dc)
There are almost 100 types of 'barrel' in use - pick one, then we can answer your question
1 dm3 is equal to 1 liter. They are equivalent volumes, with 1 liter being the same as 1 cubic decimeter.
1 liter is 1000 milliliters.