How Do You Calculate Scale Ratio in AutoCAD?

In AutoCAD, scale ratio is a crucial aspect of creating accurate and precise drawings. It allows you to determine the relationship between the size of objects in the drawing and their real-world dimensions. Understanding how to calculate scale ratio is essential for designers, architects, and engineers who work with AutoCAD on a regular basis.

What is Scale Ratio?

Scale ratio refers to the proportional relationship between the dimensions of an object on paper or screen and its actual size. It helps you maintain consistency and accuracy when transferring real-world measurements onto a smaller drawing space.

The Importance of Scale Ratio in AutoCAD

AutoCAD is widely used in various industries where precision matters. Whether you’re designing a building, creating mechanical parts, or planning a layout, maintaining accurate scale ratios is crucial. It ensures that your drawings are not only visually appealing but also practical for implementation.

Calculating Scale Ratio in AutoCAD

To calculate scale ratio in AutoCAD, you need to know two values:

  • The desired size or dimension of an object in the drawing (D)
  • The corresponding real-world size or dimension (R)

Once you have these values, follow these steps:

  1. Determine the units used in your drawing (inches, feet, millimeters, etc.)
  2. Convert the desired size (D) and the corresponding real-world size (R) into the same unit if they are different.
  3. Divide the desired size (D) by the corresponding real-world size (R).
  4. Simplify or convert this ratio into a more manageable form if necessary.

Let’s look at an example:

Suppose you want to draw a room that measures 20 feet in length (D) using a scale of 1/50. The real-world dimension (R) would be 20 feet.

To calculate the scale ratio:

  1. The units in this case are feet.
  2. Since both the desired size (D) and the corresponding real-world size (R) are already in feet, no conversion is required.
  3. Divide the desired size (D) by the corresponding real-world size (R):

Scale Ratio = D / R = 20 / 20 = 1

In this case, the scale ratio is simply 1, indicating a 1:1 scale where one unit in the drawing equals one unit in real life. This means that each foot on your drawing represents one actual foot.

Using Scale Ratio in AutoCAD

Once you have determined the scale ratio, you can apply it to your AutoCAD drawing. Here’s how:

  1. Select all objects or layers that you want to resize.
  2. Type “SCALE” into the command line or access it from the Modify panel.
  3. When prompted for a base point, choose an appropriate reference point for scaling.
  4. Enter “R” for reference length and specify a distance on your drawing that matches the corresponding real-world dimension you used to calculate the scale ratio.
  5. Enter “S” for scale factor and input the calculated scale ratio determined earlier.

Your selected objects will now be scaled based on the specified ratio, ensuring accurate representation.


Calculating scale ratio in AutoCAD is essential for maintaining accuracy and precision in your drawings. By understanding the concept of scale ratio and following the steps outlined above, you can ensure that your designs are scaled correctly and accurately represent real-world dimensions.

Remember, practice makes perfect. The more you work with scale ratios in AutoCAD, the more comfortable you will become in creating accurate and professional drawings.