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

Input:
Question: This appears to be very short (only three shelves). But in other photos it appears taller (with more shelves). How tall is this? Can you add shelves?
Document: I bought this little unit to add additional storage to my kitchen. It slides perfectly right between my refrigerator and my wall. It's a lot smaller than I imagined, but it works for what it's supposed to do. It could be longer and taller, but I think you can always add more shelves to it to make it taller. It seems like it will be durable and last a long time. It's incredibly easy to put together. It took two minutes.
We had packs of bottled water stacked on the floor by the fridge. Can't tell you how many times I tripped over it trying to get by it. I had very little space available there and didn't know what the answer was to the problem. Finally, at the end of my rope, I found this narrow cart and took a chance. It worked perfectly! It's about 5 inches wide, with three shelves. It's made out of a sturdy plastic and stands 30" tall and 21 +" deep.
I measured this at 22 inches wide, 25 inches tall and 5 inches deep. As an interesting addition, you can buy more then one and make this a taller, 50 inches, unit to hold spices, foil bag mixes, and wrap boxes.
The only reason I give this 4 stars and not 5 is because I really wish the sides of each shelf were a couple inches taller. Also if they had a taller version (overall height w/ maybe an additional 2 shelves) that would be even better. Either way, I highly recommend this item.
I downsized my 'fridge last week -- which left me with an awkward 5.5" space between the new appliance and cabinet. I saw this product, read a few reviews (as the product size was not clear from the product description) and promptly bought two because another purchaser said they could be combined into a taller rack. I put them together in less than 10 minutes; filled the shelves with spices, cooking oils, smoothie powders, coffee grinders, etc.
This unit is very easy to assemble and fit the tiny space between my washer and dryer perfectly. It rolls out easily, which is very convenient. The only reason I am giving it three starts is because one of the shelves arrived cracked. I know I could have returned it, but I still was able to assemble it without problems and the crack didn't affect the stability of the unit. I just have that section face the wall so it's not an eyesore.
After buying one to place in an awkward space between my cabinet and fridge (to store cereal boxes). I was so happy with this simple device that I bought another one for the space in my bathroom next to my sink for easy access to products since my under-cabinet is so small and undefined. It is large enough for my cereal, and the lip on the sides of the shelves are tall enough to hold my makeup and hair products. Both wipe down easily and roll out smoothly.
"Now this might be my mistake for not reading the information close enough, but I honestly thought that this item would be taller and longer. I will only be able to put MAYBE half of what I planned on it.
This works perfectly beside my fridge; easy to assemble; holds more items than I would have imagined, and is very sturdy. If there was a taller unit available, I would order it.I made the decision to purchase this based on positive reviews from Amazon.
I am short so this is just what I need to get my spices arranged so that I could reach them easily. It fits perfectly between my cabinet & refrigerator. It also holds cooking oils that are needed nearby the stove.
Answer: The unit is 29 1/2 inches tall.  It is a VERY slim unit that fits between my bathroom vanity and the toilet (the shelves are very shallow and will not accommodate a double roll of toilet paper.)  I am quite pleased with it because I use it to store small bathroom items, but I hesitate to recommend for laundry supplies or other heavy items.  As far as adding shelves:  the design has 3 shelves and there is a definite top and bottom shelf.  If you bought an additional unit and tried to combine, you'd only be able to add the center shelf from the new unit.  In addition, this is a very lightweight unit and might become unstable with any additional shelf.