M holds 1,077 names, which ties it for the largest initial here, and it averages 68 registrations each — which is essentially the catalogue's own figure. It is the biggest letter and the most average one at the same time. Whatever the catalogue does, M does at scale.
The doubled names
Mimi, Millie, Minnie, Mickey, Molly, Maggie. M produces more repeated-syllable and near-repeated names than any other letter, and the reason is physical: M is the sound a mouth makes when it is closed, which is the first consonant most children produce and the one that doubles most naturally.
Soft, and female-leaning
403 of the letter classifies soft-sounding, and 338 measure female against 292 male. A nasal consonant has no edge on it at all, and the letter's character follows from that more than from any of the names in it.
Where the outliers are
Against all that softness sits Max, the letter's most registered name and a hard closed monosyllable, along with Moose, Mack and Milo. 137 of the letter is a single syllable. M is large enough to contain its own contradiction, which the smaller letters are not.
What are the most popular pet names starting with M?
Max, Maya, Millie, Murphy and Marley lead the list, which is ordered by registrations across eleven public registers.
Why are there so many M pet names?
1,077 of them, tying M for the largest letter in the catalogue. It is the easiest consonant to produce and the one that doubles most readily, which is why so much of the letter is Mimi, Millie and Minnie.
Are M names soft?
Mostly — 403 of the letter classifies soft-sounding, because a nasal consonant has no hard edge. Max and Moose are the letter's counterexamples.
Every count on this site is a tally of real registrations: pet licences and shelter intakes published as open data by New York, Seattle, Austin, Montgomery County, Cambridge, Zurich, Basel and four Australian councils. Popularity here is the average share a name holds across those registers, so a name common in a small city is not buried by one common in a large one. Five of the eleven registers are North American and they supply 86% of the records, so read the ordering as naming in those places rather than worldwide. Browse the whole catalogue or read how the data is put together.