Kilograms to Libras (Castilian) (kg to libra)

1 kilogram equals 2.173473624 libras (Castilian) (rounded).

1 kilogram = 2.173473624 libras (Castilian)

How to convert kilograms to libras (Castilian)

To convert kilograms to libras (Castilian), multiply the number of kilograms by 2.173473624. The factor is rounded to 10 significant digits. To go the other way, multiply libras (Castilian) by 0.460093.

libras (Castilian) = kilograms × 2.173473624

Example: 10 kilograms = 21.73473624 libras (Castilian).

Approximate value. Standards for the libra (Castilian) varied by place and period, so this converter uses the most commonly cited value. Treat results as estimates, not exact figures.

About these units

Kilogram (kg)

Metric (SI)Current unit

The SI base unit of mass. Since 2019 it is defined by fixing the value of the Planck constant, replacing the old platinum-iridium cylinder in Paris.

Oddly for a base unit, the kilogram began life as a derived one. In 1793 revolutionary France defined the grave as the mass of one litre of water, and a decree of 1795 then replaced it with the kilogramme, a name built from the Greek khilioi (a thousand) and gramma, a Late Latin word for a small weight. In 1799 a platinum cylinder, the Kilogramme des Archives, became the physical standard, matching a cubic decimetre of water at its densest, around 4 degrees Celsius. In 1889 the metric community adopted a platinum-iridium cylinder made in 1879, the International Prototype of the Kilogram, nicknamed Le Grand K.

The kilogram is still the only SI base unit with a prefix in its name. Because SI forbids stacked prefixes, a millionth of a kilogram is a milligram rather than a microkilogram, so every mass prefix is attached to the gram. Calibrating every national standard against one object in a vault near Paris meant that all of them drifted relative to it, so in November 2018 member states voted to tie the kilogram to a fixed value of the Planck constant. The change took effect on 20 May 2019. Day to day nothing shifted, but the definition no longer depends on a single piece of metal.

The kilogram is the reference unit for weight & mass on this site.

Sources: NIST: Kilogram introduction (SI redefinition); Wikipedia: Kilogram

Libra (Castilian) (libra)

Spanish & PortugueseHistorical unit (no longer in standard use)Approximate value

About 460.09 g, the Castilian pound. The Spanish libra and arroba were used throughout Spain and its colonies.

Latin libra, a pound, gave Castilian Spanish its basic weight, subdivided into 16 onzas of about 28 g each. Castile kept the unit through the Middle Ages, and the national standard enacted in 1801 fixed it at exactly 0.460093 kg, the figure used here. That is about 460 g, a little more than a half-ounce above the avoirdupois pound.

Before and after that decree, local libras differed a great deal. Huesca used one near 0.351 kg, Pontevedra one near 0.579 kg, and apothecaries in Barcelona used a medicinal libra of only 0.300 kg. Standardization on paper did not remove these customs quickly, so merchants had to know which city's pound a price referred to.

Larger Castilian weights were built from the libra. The arroba was 25 libras, about 11.5 kg, and the quintal 100 libras, about 46 kg. These were used for wool, olive oil, tobacco, silver and other goods across Spain and its American colonies until metric weights replaced them in the nineteenth century, though the libra survives informally as the pound in Latin America.

1 libra (Castilian) = 0.460093 kilograms (approximately).

Sources: Wikipedia: Spanish customary units; Wikipedia: Arroba

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