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SI - The Metrics International System of Units

The International System of Units (SI) is a modernised version of the metric system established by international agreement.

SI provides a logical and interconnected framework for all measurements in science, industry, and commerce.
The metric system is much simpler to use than the existing English system since all its units of measurement are divisible by 10.

Conversion Factors

The following list provides the conversion relationship between Imperial customary units and SI (International System ) units. The proper conversion procedure is to multiply the specified value on the left by the conversion factor exactly as given below and then round to the appropriate number of significant digits desired. For example, to convert 11.4 ft to metres: 11.4 X 0.3048 = 3.47472, which rounds to 3.47 metres. Do not round either value before performing the multiplication, as accuracy would be reduced.

Conversion Symbols

The prefixes and symbols listed below are commonly used to form names and symbols of the decimal multiples and sub multiples of the SI units.

INTERIM UNITS OF MEASURE EQUIVALENT
ACRE hectare (ha)
CUBIC FOOT cubic metre (m3)
CUBIC YARD cubic metre (m3)
GALLON/MGALLON litre (L), cubic metre (m3)
HUNDRED Hundred for traffic buttons
HUNDRED WEIGHT kilogram (kg)
LINEAR FOOT meter (m)
MBOARD FEET cubic meter (m3)
MILE kilometer (km)
NAUTICAL MILE Nautical Mile
POUND kilogram (kg) for mass
newton (N) for force
SQUARE FOOT square meter (m2)
SQUARE YARD square meter (m2)
TON tonne (t)

UNITS OF MEASUREMENT USED IN SPECIAL PROVISIONS
GAGE GAUGE METAL THICKNESS gage (mm)
FAHRENHEIT TEMPERATURE kelvin (K) or degree Celsius (C)
FATHOM WATER DEPTH meter (m)
FOOT/LBS TORQUE newton-meter (N-m)
LBS/SQ. IN PRESSURES kilopascal (kPa)
megapascal (MPa) (if very large number)
LBS/SQ. FT   kilopascal (kPa)
LBS/SQ YD   kilopascal (kPa)
INCH LINEAR millimeter (mm)
KIPS;KSI TENSION kilopascal (kPa) or megapascal (MPa)
LBS/ACRE EROSION CONTROL kilograms/hectare
LBS/CU. FT. DENSITY kilogram per cubic meter (kg/m3)
MIL THICKNESS micrometer (um)
FT. LBS./SEC. HORSE POWER watt (W)

UNITS OF MEASUREMENTS USED ON CONTRACT PLANS
DEGREES/BEARINGS No change for surveying.
STATIONING 1,000 meters = 1 station
MILEPOSTS Still under review as mileposts are part of the signing issue.
Use mileposts for now, but also state kilometerposts.
ELEVATIONS meter (m)
UNITS OF MEASUREMENT USED IN COMMERCIAL STANDARDS
GALS/HR or MIN (PUMPS) liters per second (L/s)
500 GALLON TANKS cubic meter (m3) but it could also possibly be in liter (L)
55 GALLON DRUMS cubic meter (m3) or liter (L) for liquid
94 LBS/SACK (CEMENT) kilogram (kg)
DIAMETER OF REINFORCING STEEL millimeter (mm)
LBS/FT OF REINFORCING STEEL kilogram per meter (kg/m)
BUSHEL cubic meter (m3)

Length Conversion Factors
To convert from to multiply by
mile (US Statute) kilometer (km) 1.609347
inch (in) millimeter (mm) 25.4 *
inch (in) centimeter (cm) 2.54 *
inch (in) meter (m) 0.0254 *
foot (ft) meter (m) 0.3048 *
yard (yd) meter (m) 0.9144 *

Area Conversion Factors
To convert from to multiply by
square foot (sq ft) square meter (sq m) 0.09290304 E
square inch (sq in) square meter (sq m) 0.00064516 E
square yard (sq yd) square meter (sq m) 0.83612736 E
acre (ac) hectare (ha) 0.4047

Volume Conversion Factors
To convert from to multiply by
cubic inch (cu in) cubic meter (cu m) 0.00001639
cubic foot (cu ft) cubic meter (cu m) 0.02831685
cubic yard (cu yd) cubic meter (cu m) 0.7645549
gallon (gal) litre 4.546
Canadian liquid
gallon (gal) cubic meter (cu m) 0.004546
gallon (gal) litre 3.7854118
U.S. liquid**
gallon (gal) cubic meter (cu m) 0.00378541
fluid ounce (fl oz) milliliters (ml) 29.57353
fluid ounce (fl oz) cubic meter (cu m) 0.00002957

Force Conversion Factors
To convert from to multiply by
kip (1000 lb) kilogram (kg) 453.6
kip (1000 lb) newton (N) 4,448.222
pound (lb) avoirdupois kilogram (kg) 0.4535924
pound (lb) newton (N) 4.448222

Pressure or Stress Conversion Factors
To convert from to multiply by
kip per square inch (ksi) megapascal (MPa) 6.894757
pound per square foot (psf) kilogram per square meter (kg/sq m) 4.8824
pound per foot (psf) square pascal (Pa) 47.88
pound per inch (psi) square pascal (Pa) 6,894.757
pound per inch (psi) square megapascal (MPa) 0.00689476

Mass Conversion Factors
To convert from to multiply by
pound avoirdupois (lb) kilogram (kg) 0.4535924
ton, 2000 lb kilogram (kg) 907.1848
grain kilogram (kg) 0.0000648
Mass (weight) per length
kip per linear foot (klf) kilogram per meter (kg/m) 0.001488
pound per linear foot (plf) kilogram per meter (kg/m) 1.488
Mass per volume (density)
pound per cubic foot (pcf) kilogram per cubic meter (kg/cu m) 16.01846
pound per cubic yard (lb/cu yd) kilogram per cubic meter (kg/cu m) 0.5933

Temperature Conversion Factors
Temperature
degree Fahrenheit (F) degree Celsius (C) tc=(tF-32)/1.8
degree Fahrenheit (F) kelvin (K) tk = (tF+459.7)/1.8
kelvin (K) degree Celsius (C) tc=tk-273.15
Energy and heat
To convert from to multiply by
British thermal unit(Btu) joule (J) 1055.056
calorie (cal) joule (J) 4.1868E
Btu/degree F x hr x ft2 W/m2 - degree K 5.678263
kilowatt-hour (kwh) joule (J) 3,600,000E
British thermal unit per pound (Btu/lb) calories per gram (cal/g) 0.55556
British thermal unit per hour (Btu/hr) watt (W) 0.2930711

Power Conversion Factors
horsepower (hp) (550 ft-lb/sec) watt (W) 745.6999 E
mile per hour (mph) kilometer per hour(km/hr) 1.60934
mile per hour (mph) meter per second (m/s) 0.44704
darcy centimeter per second (cm/sec) 0.000968
feet per day (ft/day) centimeter per second (cm/sec) 0.000352
*indicates that the factor given is exact.
**One U.S. gallon equals 0.8327 Canadian gallon.
t--A pascal equals 1.000 newton per square meter.
Note:
One U.S. gallon of water weighs 8.34 pounds (U.S.) at 60 degrees F.
One cubic foot of water weighs 62.4 pounds (U.S.).
One milliliter of water has a mass of 1 gram and has a volume of one cubic centimeter.
One U.S. bag of cement weighs 94 lbs.

More Useful Conversion Factors
From English units To Metric units Multiply by
Length
mile km 1.609347
yard m 0.9144**
foot m 0.3048**
inch mm 25.40**
Area
square mile km2 2.590
acre m2 4047
acre hectare 0.4047
square yard m2 0.8361
square foot m2 0.092 90
square inch mm2 645.2
Volume
acre foot m3 1 233
cubic yard m3 0.7646
cubic foot m3 0.028 32
cubic foot L (1000 cm3) 28.32
100 board feet m3 0.2360
gallon L (1000 cm3) 3.785
Mass
lb kg 0.4536
kip (1000 lb) metric ton (1000kg) 0.4536
Mass/unit length
plf kg/m 1.488
Mass/unit area
psf kg/m2 4.882
Mass density
pcf kg/m3 16.02
Force
lb N 4.448
kip kN 4.448
Force/unit length
plf N/m 14.59
klf kN/m 14.59
Pressure, stress, modules of elasticity
psf Pa 47.88
ksf kPa 47.88
psi kPa 6.895
ksi MPa 6.895
Bending moment, torque, moment of force
ft-lb N-m 1.356
ft-kip kN-m 1.356
USEFUL CONVERSION FACTORS
From English Units To Metric Units Multiply by*
Moment of mass
lb . ft kg . m 0.1383
Moment of inertia
lb . ft2 kg . m2 0.042 14
Second moment of area
in4 mm4 416 200
Section modulus
in3 mm3 16 390
Power
ton (refrig) kW 3.517
Btu/s kW 1.054
hp (electric) W 745.7
Btu/h W 0.2931
Volume rate of flow
ft3/s m3/s 0.028 32
cfm m3/s 0.000 471 9
cfm L/s 0.4719
mgd m3/s 0.0438
Velocity, speed
ft/s m/s **0.3048
Acceleration
f/s2 m/s2 0.3048
Momentum
lb . ft/sec kg . m/s 0.1383
Angular momentum
lb . ft2/s kg . m2/s 0.04214
Plane Angle
degree rad 0.01745
  mrad 17.45
* 4 significant digits
**denotes exact conversion

Pavement Conversion Factors
ROADWAY DIMENSIONS BRIDGE HT. PCCP Thickness' RESILIENT MODULUS
  ft m ft m (inches) (mm) psi MPa
Lane 12 3.6 14.5 4.4 9 225 3,000 21
Shoulder 4 1.2 16.0 4.9 10 250 4,000 28
  10 3.0     11 275 5,000 34
          12 300 10,000 69
              12,000 83
              15,000 103
              20,000 138
TYPICAL DENSITY VALUES AXLE LOADS TYRE LOADS (per tyre width)
  pcf kg/m2 lbs kN lbs/inch kg/mm
PCCP 150 2403 18,000 80 500 9
ACP depth 137/0.10' 2439        

TYPICAL QUANTITIES
Asphalt Concrete Paving Quantities (metric tons/kilometer)
Depth of Pavement
  (ft) 0.10 0.15 0.20 0.25 0.30 0.35 0.40 0.45 0.50 0.55 0.60 0.65 0.70 0.75
  (mm) 30 45 60 75 90 105 120 135 150 165 180 195 210 225
Width of
Pavement		  
(ft) (M) Metric tons per kilometer
4 1.2 88 132 176 219 263 307 351 395 439 483 527 571 614 658
6 1.8 132 198 263 329 395 461 527 593 658 724 790 856 922 988
8 2.4 176 263 351 439 527 614 702 790 878 966 1,053 1,141 1,229 1,317
10 3.0 219 329 439 549 658 768 878 988 1,097 1,207 1,317 1,427 1,536 1,646
11 3.3 241 362 483 604 724 845 966 1,086 1,207 1,328 1,448 1,569 1,690 1,811
12 3.6 263 395 527 658 790 922 1,053 1,185 1,317 1,448 1,580 1,712 1,843 1,975
22 6.6 483 724 966 1,207 1,448 1,690 1,931 2,173 2,414 2,655 2,897 3,138 3,380 3,621
24 7.2 527 790 1,053 1,317 1,580 1,843 2,107 2,370 2,634 2,897 3,160 3,424 3,687 3,950
Based on 2439 kg/m3 ; 30 mm compacted depth = 73.17 kg/m2

Pavement Marking Conversion Chart
Wet Material Thickness Edge Line Coverage Area Coverage
English mils (0.001") Metric mm(0.001M) English Ft/gal Met./Eng. M/gal Metric M/Litre English SF/gal Met./Eng. SM/gal Metric SM/Litre
1.0 0.025 4832 1473 393.7 1611 150 39.37
10.0 0.254 483 147 39.4 161 15 3.94
15.0 0.381 322 98.2 26.2 107 10 2.62
19.7 0.500 245 74.8 20.0 82 7.6 2.00
20.0 0.508 242 73.6 19.7 81 7.5 1.97
25.0 0.635 193 58.9 15.7 64 6.0 1.57
30.0 0.762 161 49.1 13.1 54 5.0 1.31
35.0 0.889 138 42.1 11.2 46 4.3 1.12
39.4 1.000 123 37.4 10.0 41 3.8 1.00
40.0 1.016 121 36.8 9.8 40 3.7 0.98
45.0 1.143 107 32.7 8.7 36 3.3 0.87
49.2 1.250 98 29.9 8.0 33 3.0 0.80
50.0 1.270 97 29.5 7.9 32 3.0 0.79
59.1 1.500 82 24.9 6.7 27 2.5 0.67
60.0 1.524 81 24.5 6.6 27 2.5 0.66
78.7 2.000 61 18.7 5.0 20 1.9 0.50
88.6 2.250 55 16.6 4.4 18 1.7 0.44
90.0 2.286 54 16.4 4.4 18 1.7 0.44
98.4 2.500 49 15.0 4.0 16 1.5 0.40
100.0 2.540 48 14.7 3.9 16 1.5 0.39
118.1 3.000 41 12.5 3.3 14 1.3 0.33
120.0 3.048 40 12.3 3.3 13 1.2 0.33
236.2 6.000 20 6.2 1.7 7 0.6 0.17
250.0 6.350 19 5.9 1.6 6 0.6 0.16
255.9 6.500 19 5.8 1.5 6 0.6 0.15
260.0 6.604 19 5.7 1.5 6 0.6 0.15

Sheet Metal Conversion Factors
Most specification references use gage number followed by the decimal inch thickness. Metric specifications use the absolute mm thickness. This chart can be used to specify sheet metal. The thickness under Specify is thinner than the actual gage thickness, since specifications give minimum thickness.
Gage Inch Exact (mm) Specify (mm) % thinner than "Exact" value
32 0.0134 0.3404 0.34 0.1
30 0.0157 0.3988 0.39 2.2
28 0.0187 0.4750 0.47 1.1
26 0.0217 0.5512 0.55 0.2
24 0.0276 0.7010 0.70 0.1
22 0.0336 0.8534 0.85 0.4
20 0.0396 1.0058 1.0 0.6
18 0.0516 1.3106 1.3 0.8
16 0.0635 1.6129 1.6 0.8
14 0.0785 1.9939 1.9 4.7
12 0.1084 2.7534 2.7 1.9
10 0.1382 3.5103 3.5 0.3
8 0.1681 4.2697 4.2 1.6

Reinforcing Steel Conversion Factors
This table lists the current customary rebar sizes in relationship to the respective diameters and cross-sectional areas.
  English System Metric Equivalent
Designation No. Diameter (in.) Area (in2) Diameter (mm) Area (mm2)
3 0.375 0.11 9.5 71
4 0.500 0.20 12.7 127
5 0.625 0.31 15.9 198
6 0.750 0.44 19.1 285
7 0.875 0.60 22.2 388
8 1.000 0.79 25.4 507
9 1.125 1.00 28.6 641
10 1.270 1.27 32.3 817
11 1.410 1.56 35.8 1007
14 1.693 2.25 43.0 1452
18 2.257 4.00 57.3 2581

Wire Conversion Factors
SEVEN-WIRE, UNCOATED STRAND FOR PRESTRESSED CONCRETE STRUCTURES
This conversion for 270 GRADE LOW-RELAXATION ASTM A-416 is utilised worldwide.
Nominal Strand diameter Minimum Strength Area
(mm) (in.) (kN) (lb.) (mm2) (in2)
10 (3/8) 102.3 (23,000) 54.8 (0.085)
11 (7/16) 137.9 (31,000) 74.2 (0.115)
12 (15/32) 160.1 (36,000) 85.8 (0.133)
13 (1/2) 183.7 (41,300) 98.7 (0.153)
14 (9/16) 230.0 (51,700) 123.9 (0.192)
15 (3/5) 260.6 (58,600) 140.0 (0.217)

Hard Conversions for Construction Materials
Structural Steel, M270
  Min. Tensile Strength Min. Yield Strength Min. Yield Strength
Grade (MPa) (MPa) (ksi)
36 400 250 36
50 450 345 50
50W 485 345 50
70W 620 480 70

Reinforcing Bars, M31M
Grade Tensile and Yield Strengths
Metric value English value Tensile Strength (MPa) Min. Yield Strength (MPa) Min. Yield Strength (ksi)
300 40 500 300 40
400 60 600 400 60

Common Concrete Strengths (f'c)
Metric (MPa) 20 28 35 43 48 55
English (psi) 3000 4000 5000 6000 7000 8000

Coefficient of Thermal Expansion
  Metric Value English Value
Steel 0.0000117/oC 0.0000065/oF
Concrete 0.0000108/oC 0.000006/oF

Unit Weights
  Metric Value English Value
Steel 7848.3 kg/m3 490 pcf
Concrete 2402.5 kg/m3 150 pcf

THE CONSTRUCTION TRADES
Here are the metric units that will be used by the construction trades. The term "length" includes all linear measurements - length, width, height, thickness, diameter, and circumference.
  Quantity Unit Symbol
Surveying length kilometer, meter km, m
area square kilometer km2
hectare (10,000 m2) ha
square meter m2
plane angle degree (non metric) o
minute (non metric) '
second (non metric) "
volume cubic meter m3
Transport distance kilometer km
volume cubic meter m3
mass metric ton (1000 kg) t
Paving length meter, millimeter m, mm
area square meter m2
Concrete length meter, millimeter m, mm
area square meter m2
volume cubic meter m3
temperature degree Celsius oC
water capacity litre (1000cm) L
mass (weight) kilogram, gram kg, g
cross-sectional area square millimeter mm2

Pipe Conversion Factors
NPS DN NPS DN
1/8" 6 mm 8" 200 mm
3/16" 7 mm 10" 250 mm
1/4" 8 mm 12" 300 mm
3/8" 10 mm 14" 350 mm
1/2" 15 mm 16" 400 mm
5/8" 18 mm 18" 450 mm
3/4" 20 mm 20" 500 mm
1" 25 mm 24" 600 mm
1-1/4" 32 mm 28" 700 mm
1-1/2" 40 mm 30" 750 mm
2" 50 mm 32" 800 mm
2-1/2" 65 mm 36" 900 mm
3" 80 mm 40" 1000 mm
3-1/2" 90 mm 44" 1100 mm
4" 100 mm 48" 1200 mm
4-1/2" 115 mm 52" 1300 mm
5" 125 mm 56" 1400 mm
6" 150 mm 60" 1500 mm
(For pipe over 60 inches, use 1 inch equals 25 mm)

PROPOSED METRIC CSP DIAMETER SIZES
Proposed Metric (mm) Current Standard (inches)
150 6
200 8
250 10
300 12
375 15
450 18
525 21
600 24
675 27
750 30
825 33
900 36
1050 42
1200 48
1350 54
1500 60
1650 66
1800 72
1950 78
2100 84
2250 90
2400 96
2550 102
2700 108
2850 114
3000 120
3150 126
3300 132
3450 138
3600 144

CORRUGATION SIZES
CURRENT (Inches) PROPOSED (Millimetres)
2 2/3 x 1/2 68 x 13
3 x 1 76 x 25
5 x 1 125 x 25
3/4 x 3/4 x 7 1/2 19 x 19 x 191
3/4 x 1 x 11 1/2 19 x 25 x 292

PIPE WALL THICKNESS
CURRENT GAGE NOMINAL Thickness (Inches) PROPOSED NOMINAL Thickness (mm)
16 0.064 1.6
14 0.079 2.0
12 0.109 2.8
10 0.138 3.5
8 0.168 4.3

PIPE ARCH SIZES
Corrugations Corrugations Corrugations
Inches
2 2/3x1/2
Span x Rise		 Milllimetres
68x13
Span x Rise		 Inches
3x1 & 5x1
Span x Rise		 Millimetres
76x25 & 125x25
Span x Rise		 Inches
3/4x3/4x7 1/2
Span x Rise		 Millimetres
19x19x191
Span x Rise
17 x 13 425 x 325 53 x 41 1325 x 1025 20 x 16 500 x 400
21 x 15 525 x 375 60 x 46 1500 x 1150 23 x 19 575 x 475
24 x 18 600 x 450 66 x 51 1650 x 1275 27 x 21 675 x 525
28 x 20 700 x 500 73 x 55 1825 x 1375 33 x 26 825 x 650
35 x 24 875 x 600 81 x 59 2025 x 1475 40 x 31 1000 x 775
42 x 29 1050 x 725 87 x 63 2175 x 1575 46 x 36 1150 x 900
49 x 33 1225 x 825 95 x 67 2375 x 1675 53 x 41 1325 x 1025
57 x 38 1425 x 950 103 x 71 2575 x 1775 60 x 46 1500 x 1150
64 x 43 1600 x 1075 112 x 75 2800 x 1875 66 x 51 1650 x 1275
71 x 47 1775 x 1175 117 x 79 2925 x 1975 73 x 55 1825 x 1375
77 x 52 1925 x 1300 128 x 83 3200 x 2075 81 x 59 2025 x 1475
83 x 57 2075 x 1425 137 x 87 3425 x 2175 87 x 63 2175 x 1575
Note: millimeters equal to inches x 25.
Assumed pipe diameters will be x 25.		 142 x 91 3550 x 2275 95 x 67 2375 x 1675

Structural Plate Conversion Factors
STRUCTURAL PLATE DIMENSIONS
6 X 2 Corrugation - 31 Inch Corner Radius
Span ft-in Rise ft-in R ft. R ft.
13-3 9-4 6.68 16.05
14-11 10-2 7.48 18.98
16-6 11-0 8.29 21.93
18-1 11-10 9.09 24.98
19-8 12-8 9.90 28.04
152 x 51 Corrugation - 787 mm Corner Radius - in millimetres
Span Rise R R
4039 2845 2036 4892
4547 3099 2280 5785
5029 3353 2527 6684
5512 3607 2771 7614
5994 3861 3018 8547

STRUCTURAL PLATE THICKNESS
  Current Specification Proposed
Gage Inches Millimeters
12 .111 2.5
10 .140 3.5
8 .170 4.5
7 .188 -
5 .218 5.5
3 .249 6.5
1 .280 7.0
5/16 .318 8.0
3/8 .377 9.5

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