|3/8 inch = 1 foot (no precise metric equivalent—actual 1/32)
1/2 inch = 1 foot (1/20 or 1/25 metric equivalent—actual 1/24)
3/4 inch = 1 foot (no precise equivalent—actual 1/16)
1 inch = 1 foot (one-twelfth full size—approximate equivalent 1/10)
1 1/2 inches = 1 foot (one-eighth full size)
3 inches = 1 foot (one-quarter full size)
As an example, when used on a typical floor plan that is 1/8-inch scale, each 1/8 inch on the drawing represents 1 foot of actual size. The same applies for a 1/4-inch scale in that each 1/4-inch segment on the drawing represents 1 foot of actual size. The same approach applies to other scales.
There is no strict convention for which scale is used on which drawings, although certain parts of a set of drawings are traditionally drawn to certain scales. For example, most floor plans and elevations are in 1/8- or 1/4-inch scale, depending on the size of the building and sheet. For residential structures, the 1/4-inch scale is usually used, roughly equivalent to 1:50 in metric scale (Figure 4.5). For large commercial buildings, smaller scales may be used. Exterior elevations are often drawn to 1/4-inch scale. Sections and cross-sections may be drawn to 1/4-, 1/2-, or 3/4-inch scale if the section is complex. Depending on the amount of information presented, construction details can vary from 1/2- to 3-inch scale and even full-size scale for certain millwork details (Figure 4.6).
Civil Engineer’s Scale
The engineer’s scale is typically used to measure distance on site and land-related plans such as construction site plans, among other uses. Land measurement on site and plot plans differs slightly from measurement on building structures. It is conventional to show land measurement in feet and decimal parts of a foot, carried out to three places (55.478 feet) without the use of inches.
Most engineering scales are physically very similar and are based on the same principles as the architectural scales, except that measurements are divided into tenths, twentieths, etc., rather than halves, quarters, and eighths. The engineer’s scale has six scales: 10, 20, 30, 40, 50, and 60. Other specialty scales are divided into even small increments such as 100. The 10 scale refers to 10 feet per inch; the 20 scale is 20 feet per inch, and so on.
Sometimes the architect or engineer may include a detail strictly for visual clarification. These details are labeled “NTS” (meaning “not to scale”). This basically means that the detail is for illustration purposes only and not for extracting quantities and measurements.
According to the American National Standards Institute (ANSI), the International System of Units (SI) linear unit commonly used on drawings is the millimeter. The American National Metric Council, in its publication American Metric Construction Handbook, recommends the following with reference to metric drawings:
1. Architectural working drawings are to be dimensioned in millimeters (mm) and meters (m).
2. Plot plans and site plans are to be dimensioned in meters (m) or possibly kilometers (km), depending upon the scale, with accuracy to only three decimal places.