Sandpaper is measured by the following methods, depending on the item:
Sandpaper Belts are measured by the “width of the belt” x “length of belt” x “grit”.
That is, a 50 mm x 914 mm x 80 grit belt is 50 mm wide, 914 mm around the total circumference, and 80 grit.
Measuring a belt length
The easiest way to measure a belt is to mark the inside of the belt with a pen, put a mark on a long flat surface, bench top or garage floor. Line up the two marks and roll the belt (being careful to not let it slip on the flat surface) until the mark on the belt makes contact with the flat surface again. Put another mark on the flat surface at this point. (It is always advisable to do the process again to check your marks are correct.) Measure the distance between the two marks and you have the belt length.
Sandpaper Discs are measured across the diameter.
That is, a 150 mm diameter disc measures 150 mm across the diameter.
If a disc has a measurement of 100 mm x 16 mm, this would mean it is 100 mm in diameter and has a 16 mm centre hole. This would typically be a Fibre disc to fit an Angle Grinder and is attached by a nut secured through the 16 mm centre hole.
A sanding disc with dust extraction holes would be written as follows.
125 mm diameter x 120 grit 8 hole, or 150 mm diameter x 400 grit 7 hole.
Sandpaper Rolls are measured by the width x length x grit.
That is, a 115 mm x 50 m x 80 grit, is 115 mm wide x 50 metres in length, and 80 grit.
Sandpaper Sheets are measured by the width x length x grit.
That is, a 230 x 280 mm x 240 grit, is 230 mm wide x 280 mm in length, and 240 grit.
Sandpaper Flap Wheels are measured by the diameter x width x shaft diameter x grit.
So a 40 mm x 20 mm x 6 mm x 80 grit, is 40 mm in diameter x 20 mm wide x 6 mm shaft x 80 grit.
After these dimensions the brand and material code are usually mentioned.
For example sia 2920, Hermes RB320X, or KLINGSPOR CS321X.
In these examples sia, Hermes and KLINGSPOR are the brand, and 2920, RB320X and CS321X are the material codes.