Rarest SI Unit — All 29 Answers Ranked by Rarity

29 answers are accepted for “Name an SI unit”. Katal is the rarest SI unit in this ranking, with 8,007 monthly Wikipedia views (rarity 1.000, Legendary). Weber is the second-rarest with 45,839 monthly Wikipedia views, 5.72× the figure for Katal. Celsius is the most common SI unit in this ranking, with 378,121 monthly Wikipedia views, 47.2× the figure for the rarest. Combined monthly Wikipedia views across the 29 answers: 4,582,877. Katal is 0.2% of that total. 6 answers are Epic or Legendary: Katal (Legendary), Weber (Legendary), Henry (Epic), and 3 more.

Quick answer

Monthly English Wikipedia pageviews. Source: Wikidata + Wikipedia pageviews (2026-10).

Ranked answers

29 answers to “Name an SI unit”, rarest first. A rarity of 1 is the rarest answer in this prompt.
Rank	Answer	Tier	Rarity	Monthly Wikipedia views
1	Katal on Wikipedia	Legendary	1.000	8,007
2	Weber on Wikipedia	Legendary	0.964	45,839
3	Henry on Wikipedia	Epic	0.929	46,933
4	Steradian on Wikipedia	Epic	0.893	56,704
5	Siemens on Wikipedia	Epic	0.857	59,018
6	Becquerel on Wikipedia	Epic	0.821	79,693
7	Farad on Wikipedia	Rare	0.786	89,358
8	Candela on Wikipedia	Rare	0.750	93,236
9	Lux on Wikipedia	Rare	0.714	103,831
10	Tesla on Wikipedia	Rare	0.679	113,968
11	Lumen on Wikipedia	Rare	0.643	120,058
12	Gray on Wikipedia	Rare	0.607	127,316
13	Sievert on Wikipedia	Uncommon	0.571	135,567
14	Radian on Wikipedia	Uncommon	0.536	136,198
15	Volt on Wikipedia	Uncommon	0.500	136,521
16	Coulomb on Wikipedia	Uncommon	0.464	156,858
17	Ohm on Wikipedia	Uncommon	0.429	161,785
18	Kilogram on Wikipedia	Familiar	0.393	170,642
19	Ampere on Wikipedia	Familiar	0.357	185,590
20	Second on Wikipedia	Familiar	0.321	191,900
21	Newton on Wikipedia	Familiar	0.286	195,854
22	Hertz on Wikipedia	Familiar	0.250	207,871
23	Pascal on Wikipedia	Familiar	0.214	231,443
24	Mole on Wikipedia	Common	0.179	245,424
25	Metre on Wikipedia	Common	0.143	250,734
26	Watt on Wikipedia	Common	0.107	252,047
27	Kelvin on Wikipedia	Common	0.071	288,744
28	Joule on Wikipedia	Common	0.036	313,617
29	Celsius on Wikipedia	Common	0.000	378,121

FAQ

What is the rarest SI unit?

Katal is the rarest SI unit in this ranking, with 8,007 monthly Wikipedia views (rarity 1.000, Legendary).

How many SI units are there?

There are 29 SI units in this ranking, from Katal (rarest) to Celsius (most common).

What is the most common SI unit?

Celsius is the most common SI unit in this ranking, with 378,121 monthly Wikipedia views (Common).

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Sources

Recorded source: Wikidata + Wikipedia pageviews (2026-10). The answer list is compiled from Wikidata (CC0), and the view counts are monthly English Wikipedia pageviews. Rarity is the percentile of the popularity figure inside this prompt: 1 is the rarest and 0 is the most common. Linked names open the English Wikipedia article stored on that answer.