How to Convert Drawings to CAD

By Ryan Crooks

Hand drafted plans can be converted to CAD with a simple scale calculation.
i house plan image by Jon Le-Bon from

Computer-aided design (CAD) is a modern method of drafting. It has many advantages over traditional drawing methods, including fast editing, easy transfer and nearly universal adoption across the construction industry. However, hand drawings are still used and are an excellent form of representation. These drawings often need to be converted to CAD. Although this process takes some time and thought, most people with an understanding of scale should not have any trouble with the conversion.

Scan the drawing using a handheld or desktop scanner. Ensure the complete drawing is scanned and save it as a JPG or BMP file. You can import other file formats for many CAD programs. However, the JPG or BMP formats can be imported in nearly all applications.

Open your CAD application and start a new drawing. Click "Import" under the "File" menu and select your scanned drawing image. Place the image in the CAD drawing, but do not adjust the scale yet. A simple 1 to 1 scale ratio is fine.

Select the "Measure" tool to measure an element on the image in the CAD drawing in which you know the true dimensions. For example, a wall may measure 3/4 inch on the scanned drawing, but the wall is actually 8 feet. Record these numbers on a sheet of paper.

Calculate the amount to scale the scanned drawing by dividing the true distance by the measured distance. But remember to use the same units in the divisor and dividend. In the example, the true length is 8 feet, which is 96 inches; 96 inches divided by 3/4 inch equals 128. This is the scale factor. Also, 128 can be converted to a percentage by moving the decimal two places to the right for those programs requiring a percentage to scale---12,800 percent. Make sure you use the correct version for scaling.

Select your scanned image and click "Scale." The CAD program will prompt you to enter either the scale factor or percentage. Enter the appropriate number and press "Enter." The drawing is now drawn to its true scale in the CAD program.

Trace the scanned drawing using CAD tools, such as "Line," "Arc," and "Rectangle." Also, you may want to use other tools, such as "Offset" to produce an accurate drawing. CAD is more precise than hand drawing and errors will become apparent when the drawing is scaled in Step 5.