Birkenstock to Onitsuka Tiger shoe size

The short answer

Birkenstock 40 is Onitsuka Tiger 25.5 or 26 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 Onitsuka Tiger. EU sizes on the left, CM / JP on the right.
Birkenstock	Onitsuka Tiger, by chart	Same label	Onitsuka Tiger also prints
35	22	not published	US women's 4.5 · US men's 3 · UK 2 · EU 35
36	22.5	not published	US women's 5.5 · US men's 4 · UK 3 · EU 35.5
37	23 or 23.5	not published	US women's 6 · US men's 4.5 · UK 3.5 · EU 37
38	24 or 24.5	not published	US women's 7 · US men's 5.5 · UK 4.5 · EU 38
39	25	not published	US women's 8 · US men's 6.5 · UK 5.5 · EU 39.5
40	25.5 or 26	not published	US women's 9 · US men's 7.5 · UK 6.5 · EU 40
41	26.5 or 27	not published	US women's 10 · US men's 8.5 · UK 7.5 · EU 42
42	27.5 or 28	not published	US women's 11 · US men's 9.5 · UK 8.5 · EU 43.5
43	28.5	not published	US women's 12.5 · US men's 11 · UK 10 · EU 44.5
44	29 or 29.5	not published	US women's 13 · US men's 11.5 · UK 10.5 · EU 46
48	not made	not published	not published

Neither chart publishes the body each size is built for, so the rows line up the labels. Tinted rows change label or sit between two sizes. 1 sizes have no counterpart on the Onitsuka Tiger 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.

Open in the converter Add an item you own

Sources

Birkenstock size guide, read on 2026-09-18.
Onitsuka Tiger size guide, read on 2026-09-18. Onitsuka Tiger on TrueToSize

Onitsuka Tiger to Birkenstock