Translation:My suitcase is not as big as hers.
The expression uses "tão quanto" with adjectives and "tanto(s) quanto" for nouns.
"Quanto" can be replaced with "como" in "tão quanto".
- as + adjetivo + as
- as much + substantivo incontável + as
- as many + substantivo contável + as
'So' ought to be as acceptable as the first 'as'. It is equally as commonly used.
In English we can use "so" to replace the first "as" in negative sentences.
As good as Not so good as Not as good as.