10.05.02 calculating the scale of an image

If there is no scale present on an image/plan, use the Calculate Scale feature to determine the correct scale.

• Changing the scale of a page after performing takeoff is not recommended as On-Screen Takeoff may not be able to resize all takeoff correctly.  Some takeoff may no longer be visible on the page and or resized incorrectly.

To Calculate Scale (Using a Known Linear)

• Zoom into a line on the drawing that is labeled with its dimension (a KNOWN linear...)

• It is best to use the longest known linear on a project plan possible to calculate the most accurate scale.   

• Click Edit > Calculate Scale - the Calculate Scale dialog appears

• Select a Scale Style (Architectural, Civil or Metric)
• Enter the length of the known linear object, as displayed on the image 
• For Imperial measurements, the quantities are entered in feet and inches
• For 25', enter "2500", which is 25 feet, 00 inches
• For 100' 6", enter "10006", which is 100 feet, 06 inches
• For Metric measurements, the quantity is entered in millimeters
• For 1 meter, enter "1000"
• For 25 meters, enter "25000"

• While the Calculate Scale window is still open - click the start point, hold down the mouse button, and draw to the end point of the known linear (a red line is drawn labeled with the dimension entered for the known length)

• Notice this drawn line does not show the fractional dimension - the drawn line's label is rounded up to the nearest whole inch but the calculations are based on what is entered in the measure box

The scale automatically adjusts in the Calculate Scale window which may or may not match the existing (default) scale.

• Click OK to accept the new scale

Verifying the Scale of an Image