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Convert / Shoes

Birkenstock to Altra shoe size

The short answer

Birkenstock 40 is Altra 9 or 9.5 by the two brands' own charts.

At least one of the two brands publishes no foot length, so the rows line up the US size both charts print. Treat it as the label conversion, not a fit.

Every Birkenstock size read across to Altra. EU sizes on the left, US women's on the right.
BirkenstockBirkenstock builds it forAltra, by chartSame labelAltra builds it forAltra also prints
35not published4 or 4.5not publishedfoot length 20.5 cmUK 2 · EU 34.5
36not published5 or 5.5not publishedfoot length 21.5 cmUK 3 · EU 35.5
37not published6 or 6.5not publishedfoot length 22.5 cmUK 4 · EU 37
38not published7 or 7.5not publishedfoot length 23.5 cmUK 5 · EU 38
39not published8 or 8.5not publishedfoot length 24.5 cmUK 6 · EU 39
40not published9 or 9.5not publishedfoot length 25.5 cmUK 7 · EU 40.5
41not published10 or 10.5not publishedfoot length 26.5 cmUK 8 · EU 42
42not published11 or 11.5not publishedfoot length 27.5 cmUK 9 · EU 43
43not published12not publishedfoot length 28.5 cmUK 10 · EU 44.5
44not published13not publishedfoot length 29.5 cmUK 11 · EU 46
48not publishednot madenot publishednot publishednot published
Tinted rows change label or sit between two sizes. 1 sizes have no counterpart on the Altra chart. Read from the two charts only; no formula and no averaging.

What wearers say

Charts describe a garment. People who own both brands describe a fit, and their answer ranks above this table once five of them stand behind it. Pick your size in the converter to see whether there are enough yet.

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Sources

Altra to Birkenstock