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There are three types of scales used in architectural drawings. They are
- Architectural Scale
- Engineers Scale
- Metric Scale
An architect's scale is a specialized ruler. It is used in making or measuring from reduced scale drawings, such as blueprints and floor plans. It is marked with a range of calibrated scales (ratios). Architectural scales units are based on foot/inch dimensions. Floor plan drawings are usually drawn to the scale of 1/4" = 1'-0". For a very large plan, a scale of 1/8" = 1'-0" may be used. When drawing a small plan or a single room, scales of 3/8" = 1'-0", 1/2" = 1'-0", 3/4" = 1'-0", or 1" = 1'-0" may be used to fit the size of your drawing format. Architect scales can be read from left to right or right to left. (Figure 3)
Architect scales are used by architects to determine the actual dimensions of a distance on blueprints or scaled drawings, much like engineer scales. They are most commonly in a triangular shape with each side indicating a separate scale. All together, a triangular scale contains 11 different scales ranging from 1/4-inch-equals-1-foot scale to 1/128-inch-equals-1-foot scale. Each scale, except the 1/16 scale, are actually two scales because it can be read from left to right or from right to left. When reading from left to right, the numbers will be located closer to the outside edge. When reading form right to left, the numbers will be closer to the inside edge.
Architect's scale rulers are marked with ratios without reference to a base unit. Therefore a drawing will indicate both its scale (ratio) and the unit of measurement being used.
Typical Architectural scales used are:
- Full scale, with inches divided into sixteenths of an inch (Figure 4)
These are generally grouped in pairs using the same dual-numbered index line (one scale is read from the right, and the other scale is read from the left):
- three-inches-to-the-foot (3"=1'-0") (ratio equivalent 1:4)/one-and-one-half-inch-to-the-foot (1-1/2"=1'-0") (1:8)
- one-inch-to-the-foot (1"=1'-0") (1:12)/one-half-inch-to-the-foot (1/2"=1'-0") (1:24)
- three-quarters-inch-to-the-foot (3/4"=1'-0") (1:16)/three-eighths-inch-to-the-foot (3/8"=1'-0") (1:32)
- one-quarter-inch-to-the-foot (1/4"=1'-0") (1:48)/one-eighth-inch-to-the-foot (1/8"=1'-0") (1:96)
- three-sixteenths-inch-to-the-foot (3/16"=1'-0") (1:64)/three-thirty-seconds-inch-to-the-foot (3/32"=1'0") (1:128)
Engineers Engineering Scales units of measure are equal to parts per inch and parts per foot. The most common graduations are 10, 20, 30, 40, 50, 60 parts per inch, but there are scales available that have 100, 200, 300, 400, 500, 600 parts per foot. The graduations vary based on the application. Engineer scales are used by engineers for measuring water mains, roads and various topographical features on drawing and blueprints. Numbers run incrementally from left to right. Each inch represents a specific amount of feet. On the scale, the small lines in between the whole numbers represent individual feet. The amount of inches to feet is written in the form of 1 inch equals 10 feet or 1:10. Scales are available in a variety of graduations from 1:10 all the way to 1:600. (Figure 5)
Metric Engineering Scales - metric scale measurements is the standard in most of the world. The principles are similar. You have to get used to measurements expressed in meters (m) and millimeters (mm). One meter is slightly larger than one yard. A millimeter is 1/1000 of a meter. Metric Engineering Scales perform the same function as do engineering scales, but rather than using measurements equal to feet, they are equal to meters. The metric system is the standard measurement throughout most of the world, so it is useful for engineers to know how to use a metric scale as well as an engineering scale that uses it. Metric scales are also based on ratios, for example 1:50. (Figure 6)
Metric scales are usually based on ratios. A ratio is the relationship of one measurement to another. For example, metric plot plans are often drafted in ratios of 1:100. This scale is very close to the scale 1/8" = 1'-0" (1:96). Metric floor plans are drawn in a ratio of 1:50. This is very close to a scale of 1/4" = 1'-0" (1:48). Construction details may be drawn to metric scales of 1:20, 1:10, or 1:5. It should be noted that all dimensions in metric dimensions are in millimeters. Therefore, it is not necessary to use the symbol mm.
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