Ounce and litre both are units of measurement. Both measures quantity of liquid. The ounce is a unit of weight, volume and mass. The fluid ounce is a unit of volume. One fluid ounce is equivalent to 28.4 ml according to Imperial System and equivalent to 29.6 ml according to the US system. The abbreviation of Fluid Ounce is oz. fl., fl. oz. or fl oz . Litre is a unit of volume under the International System of Units (SI). Litre is denoted by l, L or l.

Firstly, convert the ounce to milliliters, as one oz.fl. is equivalent to 28.4 ml. Secondly, convert that resultant into litre as one ml is equal to 0.001 litre.

1 oz. fl. = 28.4ml

1 oz. fl. = ( 28.4 ml ) / (1000 ml)      …..[ since 1 ml  = 1000 litre ]

Therefore, 1 oz. fl. = 0.0284 litre

Ounce is mainly used in bartending.  During the 1824, the Parliament of Britain defined imperial gallon equivalent to the volume of ten pounds of water at standard temperature. That gallon was divided into four quarts, each quarts into two pints, each pint into four gills, and each gills into five ounce. This way there were 160 imperial fluid ounces to the  gallon. Hence making the imperial fluid ounce equivalent to 28. 4 ml.

According to the US system, US gallon is based on the wine gallon of 231 cubic inches, which was used even in Britain before 1824. After adaptation of the international inch, the US fluid ounce was equivalent to 29.6 ml.