This article summarizes the relationship between drawing scale and drawing scale factor and describes how to work with them in new and existing drawings. The article is aimed at people who create construction documentation for buildings (e.g., architectural and structural drafters) using AutoCAD.
Scales and its factors
CAD users employ two different ways of talking about a drawing’s intended plot scale: drawing scale and drawing scale factor:
- Drawing scale is the traditional way of describing a scale; for example 1/8"=1’-0" or 1=20. The measurement to the left of the equal sign or colon indicates a paper measurement and the number to the right indicates a CAD drawing and real world measurement.
- Drawing scale factor is a single number that represents a multiplier, such as 96 or 20. The drawing scale factor for a drawing is the conversion factor between a measurement on the plot and a measurement in a CAD drawing and the real world.
Obviously, the drawing scale and drawing scale factor are just two different ways of describing the same relationship. The drawing scale factor is the multiplier that changes the first number in the drawing scale into the second number.
Drawing to scale
Scaling is handled in CAD exactly the opposite from the way it is in manual drafting. In manual drafting, you squeeze real-world objects (the building perimeter, footings, 2x4s, and so on) down by a specific scale factor, like 96 or 16, so that they fit nicely on a sheet of paper. Naturally, you always draw text and other annotations the size you want them to appear on the paper (e.g., 1/8" high), regardless of the scale of the drawing.
Choosing a drawing scale factor for a new drawing
In CAD, as in manual drafting, you choose a drawing scale for a new drawing by considering the size of the sheet you’ll eventually plot on and the size of what you’re representing (e.g., a building’s plan dimensions) and.
If you know the sheet size that you’re going to use and real-world size of the building plan you’re going to draw, and you want to find out the largest drawing scale factor you can use:
- Divide the X dimension of the building by the X dimension of the sheet.
- Divide the Y dimension of the building by the Y dimension of the sheet.
- Take the larger number from the calculations in steps 1 and 2.
- Round up to the nearest "real" drawing scale factor that’s used in architectural drafting.
Determining the drawing scale factor of an existing drawing
When you plot or add text or other annotations to an existing drawing, you usually need to know the drawing’s scale factor (i.e., the multiplier corresponding to the drawing scale.) Here are some methods that you can use.