For a Gusset Bag: WIDTH X SIDE GUSSET X LENGTH 
WIDTH: Measure the length of the box, then add 2 inches 
SIDE GUSSET: Width of the box 
LENGTH: Add the height and width of the box, then add 4 inches to overlap or 8 inches to tie the bag. 

How to Measure an outer bag WIDTH X LENGTH 
WIDTH: Add the length and width of the box, then add 2 inches 
LENGTH: Add the height and width of the box then add 2 inches for ease in handling; add another 4 inches to overlap or 8 inches to tie the bag.

How to Measure a Bag Liner for Drums and Barrels
For a Flat Bag - WIDTH X LENGTH 
WIDTH: With a flexible tape measure, measure all around the drum or barrelthen divide the measurement in half. Then, add another 2 inches for ease in handling. 
LENGTH: Add the height and width of the drum or barrel. Add another 4 inches to tie the bag.

How to Measure for Pallet Covers -  For a Gusset Bag WIDTH X SIDE GUSSET X LENGTH. 
WIDTH: Measure the length of the pallet, then add another 4 inches. 
SIDE GUSSET: Width of the pallet. 
LENGTH: Measure width of pallet and divide by 2. 
then ADD this number to the height dimension, and then add another 4 inches.

How to Measure for Tubing  
Width - Measure the opening of the tubing 
DIAMETER OF PRODUCT X 1.57 (round up to the next size)