al_get_text_width man page

#include <allegro5/allegro_font.h>

int al_get_text_width(const ALLEGRO_FONT *f, const char *str)

Calculates the length of a string in a particular font, in pixels.

al_get_ustr_width(3), al_get_font_line_height(3), al_get_text_dimensions(3)

al_get_font_line_height(3), al_get_text_dimensions(3), al_get_ustr_width(3).