Backup size to fit sd card

im trying to make a gaming build using coreelec as a base and booting it off a 32 gig sd card, and im doing tar backups of my build,ive got to 15gig tar backup but when trying to restore my build on a fresh install with the tar file on a external card it says not enough space to restore build,does anyone know what the max size limit would be for a 32 gig card?, cheers