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108 THE ARCHITECTURE REFERENCE + SPECIFICATION BOOK
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Chapter 10: Measurement and geometry
The two primary measurement systems used in the world today are the metric system,
also known as the Système International d’Unités and commonly abbreviated to SI in
all languages, and the U.S. customary units system, referred to in the United States
as English units or standard units. The latter is an irregular system based on imperial
units once used in the United Kingdom and the British Commonwealth.
The metric system has become the universally accepted system of units in science,
trade, and commerce. In the United States, however, where the Metric Conversion Act
of 1975 established SI as the preferred system of weights and measures for trade and
commerce, federal laws have yet to mandate SI as the ofcial system, making its use
still primarily voluntary. Several U.S. agencies, including the American National Metric
Council (ANMC) and the United States Metric Association (USMA), are working to estab-
lish SI as the ofcial measurement system, a process known as metrication. Though
the architectural, engineering, and building trades have been slow to make a full transi-
tion, nearly all federally funded building projects are now required to be in SI units.
UNITS OF MEASURE: CUSTOMARY UNIT DATA
Customary units may be shown in a number of ways, including as fractions (1
1
/
2
) or as decimals
(1.5” or 0.125’), depending on the more common usage for a particular situation. It should be
noted that, though not the case here, exponents can be used with abbreviations that designate
area or volume; for example, 100 ft.
2
for area or 100 ft.
3
for volume.
Customary Unit Relation to Other
of Measure Customary Units
inch (in. or
)
1
/
12 ft.
foot (ft. or
)
12
in.
1
/
3 yd.
yard (yd.)
36 in.
3 ft.
rod (rd.), pole, or perch
16
1
/
2
ft.
5
1
/
2 yd.
chain
4
rd.
22 yd.
furlong
220 yd. or 40 rd.
or 10 chains or
1
/
8 mi.
mile (mi.), statute
5,280 ft. or 1,760 yd.
or 8 furlongs
mile (mi.), nautical 2,025 yd.
Customary Unit Relation to Other
of Measure Customary Units
square inch (sq. in.) 0.007
(
1
/
142
)
sq. ft.
square foot (sq. ft.) 144 sq. in.
square yard (sq. yd.)
1,296
sq. in.
9
sq. ft.
square pole
30
1
/
4 sq. yd.
acre
43,560
sq. ft.
40 rd. (1 furlong) x 4 rd. (1 chain)
square mile (sq. mi.) 640 acres
Linear Equivalents Area Equivalents
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(RAY) (Text)
Job: 03-30364 Title: Rp-Architecture Reference & Specification
#175 DTP: 216 Page: 108
Job: 03-30364 Title: Rp-Architecture Reference & Specification
#175 DTP: 216 Page: 109
(P 285U)
Fraction Decimal
1
/
32
0.03125
1
/
16
0.0625
3
/
32
0.0938
1
/
8
0.1250
5
/
32
0.1563
3
/
16
0.1875
7
/
32
0.2188
1
/
4
0.2500
9
/
32
0.2813
5
/
16
0.3125
11
/
32
0.3438
3
/
8
0.3750
13
/
32
0.4063
7
/
16
0.4375
15
/
32
0.4688
1
/
2
0.5000
17
/
32
0.5313
9
/
16
0.5625
19
/
32
0.5938
5
/
8
0.6250
21
/
32
0.6563
11
/
16
0.6875
23
/
32
0.7188
3
/
4
0.7500
25
/
32
0.7813
13
/
16
0.8125
27
/
32
0.8438
7
/
8
0.8750
29
/
32
0.9063
15
/
16
0.9375
31
/
32
0.9688
1
/
1
1.0000
Fraction to Decimal Equivalents
Customary Metric
1 in. 25.4 mm
1 ft. 0.304 8 m or 304.8 mm
1 yd. 0.914 4 m
1 mi. 1.609 344 km
Customary Metric
1 sq. in. 645.16 mm
2
1 sq. ft. 0.092 903 m
2
1 sq. yd. 0.836 127 m
2
1 acre 0.404 686 ha or 4 046.86 m
2
1 sq. mi. 2.590 00 km
2
Conversion Factors for Length
Metric Customary
1
micrometer (µm) 0.0000394 in. or 0.03937 mils
1
mm 0.0393701 in.
1
m 3.28084
ft. or 1.09361 yd.
1
km 0.621371 mi.
Conversion Factors for Length
Metric Customary
1 mm
2
0.001550 sq. in.
1 m
2
10.7639 sq. ft. or 1.19599 sq. yd.
1 ha 2.47105 acres
1 km
2
0.368102 sq. mi.
Conversion Factors for Area
METRIC CONVERSION
10
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