I often ask myself questions about strange things. You know things like "why is the sky blue?" and so forth (drives my wife and kids crazy). One question I had years ago is why are kitchen wall cabinets typically 12" deep? After all is this the most practical size for wall storage? Those of you who have large dinner plates are replying "Heck, no!"
The answer lies in how the whole idea of built in kitchen cabinets evolved and the short answer is that back in the day when carpenters and trim carpenters built cabinets on site rather than in a shop or factory they used 1 x 12 pine boards for the ends and shelves. And if you have ever bought dimensional lumber at the lumber yard you know that the "nominal" (technical term for "actual") size is 11-1/4" (3/4" lost in planing the lumber smooth and straight). These were attached to the wall with cleats and then a 1 x 2 (3/4" X 1-1/2" nominal) frame was nailed to the faces and voila! you got 12". Now 12" works fine but it wasn't because the carpenter actually engineered it that way, it was just easier to use the board in the size it was already cut to than to add to it or have to rip it down with a hand saw. Chalk it up to efficiency and practicality for the carpenter (that's the PC way of saying "lazy").
Base cabinets ended up about 24" deep for the same reason. They would use two 1 x 12 boards cleated together and add the 3/4" face frame and ended up with 23-1/4" deep. When plywood became readily available they then started cutting them to 23-1/4", added the 3/4" face frame and got 24".
Factory cabinets today are a standard 12" deep and the interior useable depth varies from 10-1/2" to 11-1/4" depending on the construction. I have done many jobs where, at the owner's request, we built the wall cabinets 13" deep to accommodate large plates and I recently did a kitchen where we made them all at 15" deep at the owner's request. Many factory cabinets offer the option of increasing the depth for an additional charge.
As an aside, if you have old job built cabinets like this, they may be made of clear old growth sugar pine or 'D' select pine or Douglas fir and are valuable pieces of wood. I have salvaged many beautiful boards through the years from old kitchens. Usually the boards were painted and had to be planed to get to the raw wood but it was worth it. Many of our early furniture in our home when I was a poor cabinetmaking apprentice were built from these boards.
This leads to other dimensional questions. Here's a few for those of you who just have to know:
Why are wall cabinets typically 18" above the counter? Because that's the way it has always been done, dingo! In truth I have no good answer other than "because it works." The only people I have seen complain about it are short people. But there is no hard-and-fast rule here. If you want them lower that can be accommodated either by lowering them or ordering longer wall cabinets. In some cases I have done jobs where we made the space taller in order to accommodate larger appliances like the old Kitchenaid mixers which wouldn't fit in the 18" space.
Why are base cabinets typically 36" high including the countertop? See the answer above. It's always been done that way and overall, except for short people, it works fine. I can see the carpenters standing in the kitchen and the carpenter's helper says, "So, boss, how high should we make these cabinets?"
Pointing to his belt the lead carpenter Joe replies, "I don't know, Bill. About this high I suppose."
"How about we ask Mrs. Smith, the owner?"
"Don't complicate things, Bill. Asking the home owner questions like that just makes our lives difficult. About 3 foot works fine, my wife is perfectly happy with that and I'm sure Mrs. Smith will be happy, too." And so here we are today... :)
Note that the appliance industry makes ranges and dishwashers based on 36" thanks to Joe's expertise. If you want your cabinets shorter consider doing one main work section rather than the whole kitchen to avoid problems with the appliances. If you want them taller again I recommend making one work area taller, not the whole kitchen because, while it will work for taller people, it can be a problem if you want to sell your home.
Is there an advantage to base cabinets deeper than 24"? This can be very nice when you want a bigger work area but in most cases 24" works fine for most people. As to storage I have found 24" deep is plenty deep and making the interior deeper is impractical for storage access.
Why are bathroom vanities 30" high? The only reason I can come up with is this goes back to the day when homes had only one bathroom and it had to accommodate the children (either that or plumbers were all short and installed the sinks lower to suit themselves!). Of course, there is only about a two year period when 30" high is the right height for kids, the rest of the time they either use a stool or bend over like the rest of us. For years we have made our vanities to the same height as the kitchen at no additional charge and most factory lines offer 34-1/2" high vanities as a standard option.
Why are bathroom vanities 21" deep instead of 24" like the kitchen cabinets? Again, because that's the way it has always been done! There is also the issue of many bathroom doors are 2'0" and you can't get the cabinet in the room. However, if you can use a 24" deep cabinet it will give you a decent amount of space behind the faucet so you don't need a toothbrush to clean back there. So, consider using kitchen cabinets in your bathroom if they will fit. Your back and your housekeeper will love you for it!
Why are factory cabinets built in 3" wide increments? This is a matter of efficiency and best use of materials and inventory. By maintaining this standard, which works in most cases (except for those dang big fillers that waste space!), they can produce the cabinets quickly and keep their costs down. Many "semi-custom" cabinet lines today, though, offer "odd" dimensions less than the 3" for additional cost (although some are now not charging extra -Showplace Cabinets for one - you just order the next largest size and specify the desired width). With our own custom cabinets we build them to any size needed since we are not working from stock parts.
I probably have missed a dimensional question here so please feel free to comment or email me and I will add it to the blog.