Pennyweights to Kilograms (dwt to kg)

1 pennyweight equals 0.00155517384 kilograms exactly.

1 pennyweight = 0.00155517384 kilograms

How to convert pennyweights to kilograms

To convert pennyweights to kilograms, multiply the number of pennyweights by 0.00155517384. This factor is exact. To go the other way, multiply kilograms by 643.0149314 (rounded).

kilograms = pennyweights × 0.00155517384

Example: 10 pennyweights = 0.0155517384 kilograms.

About these units

Pennyweight (dwt)

Troy & apothecaries'Traditional unit (still used in some regions)

One twentieth of a troy ounce (1.5552 g), originally the weight of a silver penny. Still used by jewelers.

Silver pennies gave this unit its name. In the Middle Ages an English penny weighed one twentieth of an ounce and one 240th of a pound of sterling silver, so its weight and its face value agreed. The abbreviation dwt keeps the d from denarius, the Roman coin that stood behind the old British penny.

The size changed over time. Under the medieval Tower pound a pennyweight was 32 Tower grains. When troy weights replaced Tower weights in 1527, it became 24 troy grains, which is exactly 1.55517384 grams.

Twenty pennyweights make a troy ounce, and 240 make a troy pound. Jewellers still use it to work out the precious metal content of jewellery, and dental labs have used it for gold in crowns and inlays. In parts of England, gooseberry growers also record prize fruit in pennyweights and grains.

1 pennyweight = 0.00155517384 kilograms (exactly).

Sources: Wikipedia: Pennyweight; Wikipedia: Troy weight; NIST SP 811, Appendix B.8

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

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