How to Read an Architect’s Scale

Architect’s scales are used on scale drawings.   In the video, Bob and Sparky break down the basics of using an architect’s scale.


Here is the video transcript:


The type of architect’s scale we’re going to look at is used to make measurements on a drawing that is dimensioned in feet and inches, like architectural drawings.  You see, architectural drawings like house plans are drawn to a particular scale.   In this case, a quarter inch on the drawing represents one foot in real life. The cabinets on the drawing are 12 feet 8 inches wide.  If you measured the the drawing of the cabinets with a regular ruler, you would see that they would be a little longer than 3 inches wide. To get an exact measurement we would need to do some calculations.

Here is an architect’s scale. When we use a scale like this, we don’t need to do any calculations. Architects scales are designed to work with scaled drawings.  On an architects scale, there are different marks for the foot and the inch parts of the measurement.  On one side of this zero is where you measure the feet, and on the other side is where the inches come from.

One of the keys to understanding a scale like this is to see that the part where you get the inches (the end with the small marks) is really just an oridinary 12 inch long ruler that has been shrunk down to the scale you are using. The hardest part is figuring out what each small mark means. 06) First, we want to be sure we are using the right scale. You see that this scale is labeled “one quarter.” This means that you use this scale on drawings that are drawn to a scale of one quarter inch equals a foot — like our cabinet drawing.

Let’s look at the inch part of the scale first.  Now remember that I said that the inch part of the ruler is just an ordinary 12 inch long ruler that has been shrunk down o the scale you are using? Well with this scale it is easy to see that. Look closely and count the number of marks on this teeny tiny 12 inch ruler. Let’s see…one two three four five six seven eight nine ten eleven twelve.  There, easy. Each mark represents one inch. 10) Let’s look a different scale. Let’s look at a 1/8 of an inch equals a foot. Notice that this scale is at the other end of the ruler. On this one, the inch part is on the left and the feet are on the right. 12) Now remember that we said that the inch part of an architects scale is just a 12 inch long ruler that has been shrunk down to the scale you are using.  Lets take a close look at the 12 inch ruler here and see what each mark means. Last time we said that each mark represented one inch. Well this scale is tinier than the last one, and it doesn’t seem to have as many marks. Lets count them. one two three four five six. do you see that each mark on this scale represents two inches instead of just one? Good! that’s the hardest part of using this kind of scale — figuring out what each mark on the inch part represents.

Now let’s look at one more scale. Let’s see the scale for 3/4 of an inch equals a foot. 15) First we look for the zero. and we find that here the inches are on the left and feet are on the right. We’ll remember that this part of the ruler represents a 12 inch ruler that has been shrunk down. Lets count the marks. one two.. wait a minute, that;s too many to count. lets do this a faster way.  Since we know this is a 12 inch ruler shrunk down, we know that half way is six inches. And half of that is three inches. That makes this one inch, and the smallest mark is a half inch.  I think you understand the inch part of these scales, let’s move to the easy part. Lets look at the part of the scale used to measure whole feet.  Now remember how we said that the inch part of the architects scale is a 12 inch ruler shrunk down? I thought you did.  Now remember that 12 inches equals one foot. Well look at the inch part of the ruler to see how big a foot would be at this scale…. There.  Now let’s flip that foot over and count….one two three four.  What’s that? ok, i see . Sparky said somebody is asking about the extra marks and numbers.  Those marks are counting whole feet from the other end of the scale. On this ruler, the 1/8 inch equals a foot scale is on the same part of the rule as the 1/4 inch equals a foot. You just read them from different ends. See how this scale is counting in the other direction? ,40,41,42,43,44. You can just ignore the extra marks coming from the other end of the ruler.

So let’s dive in and take some measurements. When we measure with an architects scale, we will first measure the number of feet, then slide the ruler over and measure the inches. Here, ill show you. We start by putting the item to be measured at the zero mark… count the number of whole feet. one..two..three. good, now slide the ruler over to the last whole foot……and now measure the inches. one…two…three. So the measurement is three feet three inches. Now we’re going to let you try a few. I’ll position the reading at zero then slide the ruler over and let you measure the feet and inches inches. when you see Sparky’s paws, pause the video and write down your answer.

First here is one at the same 1/4 inch equals a foot scale. Hit the pause button and think about it….. The reading is 2′-11″ did you get that? Good! lets try a harder one. We’ll try one at 1/8 inch equals a foot. Pause the video and take your time on this one. Did you say five feet four inches? If you did, you really know what you are doing. If not, lets have a look at what marks to count. See, 1,2,3,4,5 feet, and each inch mark counts as two inches. the numbers 20 and 22 are from the other side of the ruler, just ignore them.

We’ll do one more. If you get it you’ll be ready for that test tomorrow.  ok…pause the video… The correct reading is one foot, one inch. 36) Well that’s all the time we have for now. If you want more practice problems, or if i need to clear something else up just let me know… I’m Bob Welds and these are Weldnotes.

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5 Responses

  1. Cora Brown-Campbell says:

    I asked specifically for information about the 1/2″ scale and was given others and not that one.

  2. vgoop says:

    Hi, We sell Architectural Scale Ruler (imperial) in Amazon.
    We would like to put your explanation video in our listing.
    Is it OK with you?

  3. Nara says:

    Bob, I am hoping to use your video as part of a “bridge” curriculum for welding students. How can I contact you to ask?

  4. Steve C. says:

    Enjoyed the video, but I need to know how do you read the 3/8″ scale of an architectural ruler?

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