The best way to choose the right size of the bottle is to start with the extension of the space you want to scent:
250ml > 8-10 sqm*
500ml > 20-25 sqm*
The use of the sizes 1250 ml, 2500 ml and 5000 ml, surely suitable for ambiances usually larger than 15 sqm*, besides granting an effective perfume, represent a real home decor element.
*the sqm are indicative and usually refer to ambiances with high ceilings, average 2 meters height
The 100 ml diffuser is used to scent only small areas (ex. walk-in closets), the spray instead to refresh them temporarily.
In the center of a room or, for larger ambiances, it is recommended to have 2 on opposite sides of the area.