I measured my carpet as directed and chose the low-pile based on that. This mat is too soft for my carpet and the wheels on my desk chair sink in creating divots that it's hard to wheel out of. I stopped using it after a week and it's now sitting on my cellar's cement floor.
The 36" x 48" clear chair mat is the perfect size for my rolling office chair at my desk. I recommend buying one to save your carpet and making it easier to roll with a chair or have a stationary chair.
This is a good fairly priced chair mat for a person who will not be subjecting it to day in and day out heavy duty use. This particular mat will work best on a low pile carpet. For light occasional duty in a home office it will do the job and preserve the carpeting. I am satisfied with it but having used these protective mats in offices I recommend that if you need a mat that will really stand up to office heavy duty wear and tear and abuse for five days a week go with the thicker more expensive mats.
Where this mat helped my chair glide easier over my carpeting indentations from the office chair wheels occurred within 2 days of receiving. This was very disappointing. I am now rotating the mat to help even out these dips.