The word arroba has its origin in Arabic ar-rubʿ (الربع), the fourth part (of a quintal), the term defined the load that a donkey or mule could carry.
Arroba was a Portuguese and Spanish customary unit of weight, mass or volume. Its symbol is @. In weight it was equal to 32 pounds (14.7 kg) in Portugal and 25 pounds (11.5 kg) in Spain.
The unit is still used in Portugal by cork merchants, and in Brazil by cattle traders. The modern metric arroba used in these country life activities is defined as 15 kilograms (33 lb).
In Peru the arroba is equivalent to 11.5 kilograms (25 lb).
In Bolivia nationally it is equivalent to 30.46 litres (6.70 imp gal; 8.05 US gal). However locally there are many different values, ranging from 11.5 litres (2.5 imp gal; 3.0 US gal) in Inquisivi to 16 litres (3.5 imp gal; 4.2 US gal) in Baures.