Instruction: Extract information from the supporting document to answer the given question.

Input:
Question: Is the 18" measured from the outside or inside of the side rails?  I have a vent on the lower third of my door that is 17.5" wide. Will the rack fit?
Document: Since we just moved into a smaller place I needed something to put extra kitchen items on and this fit the bill. We actually mounted it to the side of the refrigerator and it works perfectly. The shelves are adjustable and hold way more than I had hoped for. Since the shelves are over 5 inches wide it was perfect for larger spice bottles and box items. I also lined the shelves with the grip type lining and it works great for holding things in place.24 Inch Wide Adjustable Door Rack Pantry Organizer
Difficult to install because the side rails were all warped and all the screw anchors had to be trimmed to fit  holes. The ends of each rack are open, so you cannot place small objects such as spice bottles there or they will fall out.
I had a very small closet door that I wanted to put this on. I looked at the measurements listed, measured the door and it look liked it would fit with 2&#34; to spare on each side. Once I received the product and went to install it, it was too big for the door!
The rack was too wide so the door wouldn't shut. I cannot use it. This is not the sellers fault, as I should have measured first
The item doesn't tell the buyer enough about the product. The rails are plastic and the baskets are made out of a light gage metal. I bought metal rails from menards and drilled them to fit. Installed a third rail down the middle and L shape angles under the basket to support heavier items. The cost increased 2 1/2 times from the original purchase but now it will hold what I want. It was either that or the garbage.
I thought this unit would be somewhat more sturdy. Side rails are cheap plastic and since the rails come in three pieces to make one upright, it was tricky to align straight up and down. the bottom of each rack/basket, does not attach to the rails, but just sets in using the weight of what might be on the shelf to secure it down once the end is seated in the upright.
Overall,now thqt the rack has been up a month, I am happy with it.When I pulled the PLASTIC rails out of the box, I groaned thinking this was just going to be a cheap fall-apart item. However, the plastic rails have held up well under full load and when it came time to trim them off to fit my needs, they cut easily with a box knife.The only disappointment I had was with the hollow wall anchors that came with it.
1. The railings that hold the shelves are plastic2. The railings that hold the shelves are 4 separate pieces that fit together but do not snap or attach to each other3. The sides of the shelves are open- anything short falls out the side4. The hangers that come with it do not have a lip & slip right into the door5. The 18" version does not fit well on a door with raised panels (ie most interior doors)6.
I was so excited to find this item as I was convinced it would add a lot to my limited pantry space. Well, I can't say how the 18" system holds up, but the 24" setup is way too flimsy. The back braces are PLASTIC (actually 4 separate units for each side that you slip together creating weak joints that pop apart) and unable to hold much weight at all without buckling (ditto for the baskets which change shape too when even a small amount of weight added).
Worked Great. I did have to pull the shelves out and cut 1 inch off so the door would close. The rack is 5 1/4 deep and the door jam and door was only 4 3/4. Thanks for a great rack and I would suggest it to family and friends.
Answer: The inside is 17", the outside is 18.5".  Good luck!