How to Calculate Drafting Dimensions

Drafting requires elements and assemblies to be drawn to a scale, and in most cases, the scale is much smaller than real scale, or 1-to-1. The scale of the drawing depends on the size of the drawing sheet, real scale of the element or assembly and the required legibility of the drawing. Although most objects can be drawn at a smaller scale, the parts of the object must be clearly rendered to facilitate understanding and construction of the object. Almost all drafted drawings include a visual or written scale, such as 1/4 inch equals 1 foot or 1 inch equals 10 feet, and you can calculate drafting dimensions using an architectural or engineering scale.

Architectural or engineering scale
Drawing sheet

Instructions

- 1
  Determine the scale of the drawing.
  
  If you are drafting the drawing, the drawn object should easily fit on your sheet. Establish the desired limits of the drawing on the sheet and find the real dimension of the object. Divide the desired drawing size by the real object size, using the same units, such as feet or inches. Find the closest standard scale to this quotient. For example, 1/4 inch equals 1 foot is 1/48 true scale, whereas 1 inch equals 10 feet is 1/120 real scale. So, if your quotient is 1/45, use 1/4 inch equals 1 foot. To calculate other scales' fraction of real scale, divide the first number by the second, using the same units. For example, 1/8 inch equals 1 foot is 1/8 inch equals 12 inches, which is 1/96 real scale.
  
  If the drawing is already drafted, find the scale on the drawing. The scale is usually in the lower right corner of the drawing or below the drawing title.
- 2
  Find the appropriate scale on your architectural or engineering scale. The scale is marked as a fraction at either end of the architectural or engineering scale. For example, 1/4 inch equals 1 foot is marked as "1/4" on one side of the scale, whereas 1 inch equals 10 feet is marked as 1/10 on one side of the scale. The ticks, or marks, on the scale are 1 foot intervals at the given scale. On the opposite side of "0" on the architectural or engineering scale, 1 foot is subdivided with additional ticks, or marks. These subdivisions are inches in a foot.
- 3
  Measure the appropriate dimension using the foot and inch marks: the use of the scale will accurately calculate the drafting dimensions.

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