Ma'anar ƙamus na "size constancy" shine yanayin fahimta inda girman abu ya kasance koyaushe ko da an duba shi daga nesa ko kusurwoyi daban-daban. Ƙwaƙwalwar ƙwaƙwalwa ce ta gane girman abu a matsayin akai-akai, ba tare da la'akari da nisa daga mai kallo ba ko girman siffar idonta. Wannan yana ba mu damar gane abubuwa a matsayin girmansu ɗaya ko da sun bayyana girma ko ƙarami saboda canje-canjen da suka samu daga nesanmu.