Brazil officially adopted the metric system back in the 19th century, but traces of old units, like the arroba and the légua, still survive in certain contexts today.
Brazil was one of the first countries in the Americas to formally adopt the Decimal Metric System, through Imperial Law No. 1,157, enacted in 1862, still during the reign of Dom Pedro II. Before that, the country used a set of units inherited from Portugal, such as the légua (league), braça (fathom), alqueire, and arroba — each with definitions that could vary slightly between regions, making trade and standardized tax collection across the territory difficult.
The transition was not immediate: the 1862 law gave merchants, farmers, and public agencies years to adapt to the new standards, and effective enforcement of the metric system only solidified in the following decades, with the creation of weights and measures agencies at the state and, later, federal level.
Interestingly, some of these old units never fully disappeared from Brazilian vocabulary. The arroba, for example, is still widely used today in cattle ranching to price livestock (1 arroba of cattle equals 15 kg of carcass weight), and the légua still occasionally appears in rural and historical contexts, even without official legal value. The alqueire, used to measure land area, still has current use in informal rural negotiations, even though its definition varies from state to state (the São Paulo alqueire and the Minas Gerais alqueire, for instance, correspond to different areas).
Today, the National Institute of Metrology, Quality and Technology (Inmetro) is the agency responsible for ensuring that measuring instruments sold in Brazil follow the International System of Units (SI), the modern, internationally standardized version of the metric system. Understanding this history helps explain why, even in a country that has officially been metric for over 160 years, you can still hear someone negotiating cattle "by the arroba" at a countryside market.
The transition to the metric system was not uniform across Brazilian territory. Large cities and formal commerce adopted the system more quickly, driven by inspection and the need for standardization in commercial transactions. Rural areas and informal commerce maintained the use of old units for much longer, especially in contexts where local tradition and the absence of inspection made the metric system less relevant to everyday life.
The alqueire is a particularly interesting example of an old unit that survives with variable definitions. The São Paulo alqueire equals 24,200 m² (2.42 hectares), while the Minas Gerais alqueire corresponds to 48,400 m² (4.84 hectares) — double. This regional variation persists in informal rural negotiations to this day, and has generated legal disputes when contracts used the term "alqueire" without specifying which state. In formal contexts, the recommendation is always to convert to hectares or square meters to avoid ambiguity.
The arroba, another historical unit of mass (originally 14.688 kg in the Portuguese system), gained a peculiar modern use in Brazil: in cattle ranching, "arroba" came to mean 15 kg of cattle carcass, and is the standard unit for pricing cattle in the market. This practical redefinition, different from the original historical value, illustrates how old units can survive adapted to new contexts. TudoConversor offers conversion between arroba, kilogram, and other units of mass and area, helping to connect these historical units with the modern metric standard.
Imperial Law No. 1,157 of 1862 was not an isolated act: it was part of a broader modernization movement in the Brazilian Empire, which in the same decade invested in telegraphs, railroads, and educational reforms. The standardization of weights and measures was seen as essential to integrate a country of continental dimensions, where the lack of uniform standards hindered tax collection and trade between provinces. The French decimal metric standard, already adopted by several European nations, was chosen for its simplicity and scientific prestige.
Inmetro, created in 1973 by Law No. 5,966, succeeded the former National Institute of Weights and Measures and considerably expanded the scope of national metrology, encompassing quality, certification, and technical regulation. Today, Inmetro maintains the International System of Units as the legal basis for all commercial transactions in the country, and its resolutions define how measuring instruments — from supermarket scales to fuel meters — must be calibrated and sealed periodically to ensure consumer trust.