A 0.5 inch above the floor
B 6-8 inches below the sill (or 1 inch above the radiator)
C 0.5 inch above the sill
Always measure in at least 3 positions across the track or pole as floors and sills are rarely level. To avoid curtains dragging across the floor or sill we recommend you use the shortest of these 3 measurements.
When measuring for curtains please use a metal tape measure as cloth or plastic tape measures may stretch. Always quote sizes in inches.