Wikipedia:Reference desk/Archives/Science/2025 August 7

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August 7

Metric prefixes

Why are there no standard metric prefixes for 10⁴, 10⁵, 10^-4 and 10^-5? I wondered that when I was younger, and invented my own for these powers. If most languages use their own words until 999,999 and -illions after that, so why metric prefixes for 10,000 and 100,000 do not exist? --40bus (talk) 07:53, 7 August 2025 (UTC)[reply]

For 10⁴, see myria-. PiusImpavidus (talk) 08:50, 7 August 2025 (UTC)[reply]

For 10^-4, see decimilli. JMCHutchinson (talk) 13:26, 7 August 2025 (UTC)[reply]

They probably weren't seen as needed when the system was created (inability to measure that finely for small scale and lack of things to measure at large scale). When it became possible to use them, the need for much larger and smaller multiples would have made such prefixes an over complication. I often wonder why centi-,deci-, deka-, and hecto- haven't been dropped.--User:Khajidha (talk) (contributions) 11:39, 9 August 2025 (UTC)[reply]

Unsurprisingly, we have a metric prefix aricle that talks a bit about the history, including the components of the original metric system that were/weren't adopted when it became then International System of Units (SI) and its later expansion with new prefixes. Expansions being increments of 10^±3 (increments of ±1000) is consistent with numbers being written with digits delimited in groups of three (the typography and current formal standards for this are covered in the decimal separator article). For an alternate formatting and naming pattern, see Indian numbering system (names and digit-breaks are every odd power of ten starting at 1000). DMacks (talk) 15:55, 9 August 2025 (UTC)[reply]

centi-, deci- and hecto- are widely used in daily life, certainly more than nano- and below or giga- and above. When I buy cheese, I ask for hectogrammes, when I measure clothing, it's in centimetres.

There's a factor 10⁹ between cubic kilometres and cubic megametres and volumes in this range are common enough that having some unit between those could be convenient. There are petalitres of course, 1000 km³, but the litre isn't really an SI unit. PiusImpavidus (talk) 20:21, 10 August 2025 (UTC)[reply]