Scale Vs Size

So, I guess I'm ne to working in 3D space but can someone pont me in the direction oh an explanation of how size and scale work and obect relate to each other. I have object that are on a diffenernt scale for each access but are still all the 30 x 30 x 30 cubes. Like, can i just turn scale off and work from size? Ive never felt stupider... I cannot figure this out.