How to Use a Drafting Scale

When making architectural drawings of a structure, a draftsman must determine a "scale" for the drawings so that they reflect the building's correct proportions. For example, a drawing might be executed at 1/4" scale so that one foot in the actual building is drawn at 1/4" in the drawing. The drafting scale is a special type of ruler that helps drafting professionals create their scale drawings accurately. Shaped like a pyramid, the drafting scale contains two different measurements on each face--one beginning at each end. Each set of measuring increments represents a different proportional scale (i.e. 1/4", 1/8", 3/16", etc). The increments in each set are numbered according to the desired measurements of the completed drawing. So, if a draftsman needs to draw a line 4 feet long at 1/4" scale, he will choose the 1/4" measuring side of the drafting scale and draw his line from "0" to the tick mark labeled "4". This tool allows a draftsman to easily create drawings at the appropriate scale without needing to actually calculate the proportional ratio. It is particularly helpful in changing the proportions of drawings required for a project. Here's how to use a drafting scale to measure one floor plan drawing and create a new one at a different scale.

Find the scale of your original drawing. It may be included in the drawing legend. If the legend does not indicate the measuring ratio, you can use an architectural element with a standard measurement, such as a window or doorway, to determine the scale by trial and error. For example, typical exterior doorways are 3 feet wide. When you locate one on your original floorplan, measure it with various sides of your drafting scale to determine which one indicates "3" for the width of the door opening. Then, look at the left end of your drafting scale on that face to find the correct proportional scale.

Decide on a scale for your resized floorplan. You can enlarge or reduce the proportions of your original drawing according to your project needs. Check each end of your drafting scale until you locate the desired measuring ratio.

Choose a starting point for your new drawing. A corner of the original drawing is a good place to begin. You will be able to create your new floorplan by measuring one line at a time on the original and drawing it at the new proportional scale on the revised floorplan.

Measure your original drawing at the starting point. Locate the side of your drafting scale that measures dimensions based on the original floorplan's proportional scale. Then, line up "0" at the corner of your starting point. Check the tick marks on the drafting scale to determine the length of the first horizontal line in your original drawing.

Create your first line on the new floorplan. With a straight edge, draw a horizontal line of any length. Then, flip your drafting scale until it shows the chosen scale for your new drawing, with "0" at the left. Line up the straight edge of the drafting scale with the horizontal line your drew. Make a light mark with your pencil at the "0" tick mark and at the tick mark of the dimension of the original floorplan's first horizontal line (determined in Step 4). Now you have your newly scaled starting point for your revised floorplan. Erase any unneeded portions of the horizontal line.

Draw in additional lines on your new floorplan. Working up and out on your original floorplan, continue to measure the first drawing line by line, drawing the corresponding lines on the new floorplan using the appropriate measuring scale. Once all of your lines are in place, you can erase any stray lines and ink in the new drawing as needed.


Create your drawing in pencil first to make measuring errors easier to correct. You can ink it in when complete. Use a small drafting dot or sticker to mark the starting end of your chosen measuring scale. That way, it's easy to flip straight to the increments you need. Be sure to include a scale legend on your new drawing so it is easy to determine the new size.


Don't make a practice of using your drafting scale as a straight edge for drawing. This will wear away the markings and shorten the life of your scale.

About the Author

Haley Montgomery is a graphic designer in Starkville, Miss., where she writes about design, marketing, website development and parenting. Montgomery earned a bachelor's degree in graphic design at Mississippi State University and has worked in the advertising industry for 15 years. Her writing has been published by BrightHub.com and RootandSprout.com. She also writes a marketing blog at DuxDLux.com.