Conversion from 100 Micrometers to Kilometers

Information about the Micrometer (μm)

The micrometre is one millionth of a metre, written µm using the Greek letter mu. It is also widely called the micron, a name the General Conference on Weights and Measures formally abolished in 1967 but which remains in everyday use across manufacturing and materials science.

The unit covers the scale of individual cells and fine particles. A human red blood cell is about 7 µm across. Bacteria typically measure 1 to 5 µm. Human hair ranges from roughly 17 to 180 µm in diameter, which is why hair is visible while cells are not. The limit of unaided human vision falls near 50 µm.

Air quality regulation relies on the micrometre. PM10 and PM2.5 refer to particulate matter smaller than 10 µm and 2.5 µm respectively. The distinction matters medically: larger particles are filtered by the nose and throat, while PM2.5 penetrates deep into the lungs and can enter the bloodstream.

Precision engineering works in the same range. Machining tolerances are commonly specified in micrometres, and surface roughness is quoted in the same unit. Bearing clearances, paint film thickness and the flatness of optical components are all measured this way. The measuring instrument called a micrometer, or micrometer screw gauge, is named for the precision it offers rather than for a fixed relationship to the unit.

Wavelengths in the infrared are usually given in micrometres rather than nanometres. Thermal imaging cameras typically operate between 8 and 14 µm, the band where objects at everyday temperatures emit most strongly.

Filtration is specified almost entirely in this unit. Water filters are rated by the smallest particle they retain, commonly between 0.2 and 50 µm, and a 0.2 µm filter is fine enough to remove most bacteria. Surgical masks and respirators are tested against particles in the same range. The N95 designation refers to a filter that captures at least 95 per cent of airborne particles at the hardest size to trap, around 0.3 µm.

Its older name still causes confusion. Until 1967 the unit was officially called the micron and written with a bare Greek mu, and the word remains common in industry even though the conference of that year removed it from the SI. Semiconductor manufacturing carried the name for a generation: chips were described by their process node in microns, falling from ten in the 1970s to below one by 1990, at which point the industry switched to nanometres and kept going. The modern node names no longer correspond to any physical dimension on the chip, but the earlier ones did, and they were quoted in exactly this unit.

One micrometre equals 1000 nanometres, 0.001 millimetres, or 10^-6 metres.

Information about the Kilometer (km)

The kilometre is one thousand metres, written km. It is the standard unit for road distance, geographic separation and travel across almost the entire world, and after the metre itself it is the most widely used SI length unit.

Road signs, speed limits, vehicle odometers and navigation systems use it in every country except the United States, Liberia and Myanmar, where miles remain in place. The United Kingdom occupies a middle position: road signs and speed limits are in miles, while most other official measurement is metric. Running and cycling events are almost universally set in kilometres, with the marathon a notable exception at 42.195 km, a distance fixed by the route used at the 1908 London Olympics rather than by any round figure.

The unit suits the human scale of travel. A brisk walk covers about five kilometres in an hour. Urban journeys are typically a few kilometres, and national distances run to hundreds or thousands. Below one kilometre metres are more natural, and above a few thousand many people switch to comparing flight times instead.

Pronunciation is contested. The stress pattern KIL-o-metre follows the pattern of other SI prefixed units such as kilogram and kilowatt, where the prefix is unstressed. The alternative, ki-LOM-eter, is nonetheless dominant in North America and common in Australia and New Zealand, and both are recorded as standard by major dictionaries.

The kilometre also anchors two other units. A square kilometre is one million square metres, or 100 hectares, and is the usual measure for the area of towns, lakes and protected land. Speed is expressed as kilometres per hour, written km/h.

Astronomy uses the kilometre for objects within the solar system, where larger units would be unwieldy. The Moon averages 384,400 km from Earth and the Sun about 149.6 million km. Beyond that distance astronomers switch to astronomical units, light years and parsecs, because the kilometre figures become too long to read. Orbital velocities are given in kilometres per second: the International Space Station travels at roughly 7.66 km/s.

One kilometre equals 1000 metres or 100,000 centimetres. It is approximately 0.621371 miles, so a five-kilometre race is a little over three miles.