This is an irregular verb. It is a model verb.
PresentPresente
Yo no quepo en estos pantalones viejos.
I don't fit in these old pants.
PreteritePretérito indefinido
Toda la ropa cupo en una sola maleta.
All the clothes fit in a single suitcase.
ConditionalCondicional
El piano no cabría por esa puerta.
The piano wouldn't fit through that door.