What size is Asics US 9 in Brooks?

About Brooks US 9 (EU 42.5), matched by ~26.1 cm. Then adjust for the specific model.

Is a Asics 9 the same as a Brooks 9?

Not always. Labels can map to different foot lengths — use cm, then model fit.

Brand-to-brand size at a fixed US label — matched by foot length (cm), not guesswork.

Asics US 9 maps to about 26.1 cm on that brand’s chart. The nearest Brooks row at that length is US 9 / EU 42.5.

Same chart cm can still feel different on foot. Read the guides:

Asics: Gel-Kayano 31 (true to size) · Gel-1130 (true to size)

Brooks: Ghost 16 (true to size) · Glycerin 21 (true to size)

What size is Asics US 9 in Brooks?: About Brooks US 9 (EU 42.5), via ~26.1 cm.
Where is the full size table?: Asics to Brooks compare.