Barleycorn
A barleycorn is an old English unit of length, traditionally based on the length of a grain of barley. It is defined as exactly 1/3 of an inch or approximately 8.47 millimeters.
Historically, the barleycorn was used for measuring small lengths and was also the basis for the inch, which was originally considered to be three barleycorns long. It played a role in various traditional measurements, including shoe sizing in English-speaking countries, where shoe sizes were sometimes expressed in barleycorn units.
Although obsolete as a formal unit, the barleycorn remains culturally significant, especially in shoe sizing systems.
Summary:
1 barleycorn = 1/3 inch ≈ 8.47 mm
Based on the length of a grain of barley
Used historically in small measurements and shoe sizing
Mostly of historical and cultural interest today
Picometer
A picometer (pm) is an extremely small unit of length in the metric system, equal to one-trillionth of a meter (1 pm = 10⁻¹² meters). Picometers are used to measure things on the atomic and subatomic scale, such as the size of atoms or the distance between particles in a molecule. For example, a hydrogen atom is about 50 picometers in radius. This unit is mainly used in physics, chemistry, and nanotechnology. Because it's so small, you won’t see picometers used in everyday life — they are only relevant in scientific research where ultra-precise measurements are required.
No conversions available for length.