General
One of the main aims of this book is to provide practical information for builders in all parts of the world. But its practical value is reduced in places where the systems of measurement differ from those in the book  and this is true for any technical book.
The two main systems of measurement are the English (Imperial) and the metric systems, and their use in each country was mainly determined by its historical development The metric system is now the official system in most of the countries that were accustomed to the Imperial system, but the change of systems has always proved to be a difficult and slow process, as the people have to readjust themselves to a new way of thinking. A further problem is that the Imperial system is still officially used in North America.
The basic units of the Imperial system are foot, pound and second, while the basic units of the metric system are metre, kilogram and second (MKS), which later also included ampere (MKSA). The inclusion of kelvin (thermodynamic temperature), mole (amount of substance) and candela (light intensity) led to a new internationally standardised system of measurement, called SIUnits (Systeme International d'Unites).
The units of measurement given in this book are mainly SIunits, as they are the most widespread. In order to make the book equally useful to those readers, who are less acquainted with the metric units, some of the most important conversion factors are given on the following pages.
IMPERIAL UNITS 
CONVERSION FACTORS 
METRIC/STUNITS 
Length 


Units: inch(in) 
1 in = 25.4 mm 
Units:millimetre (mm) 
foot(ft) 
0.39 in = 1 cm 
centrimetre (cm) 
yard(yd) 
1 ft = 30.48 cm 
metre (m) 
mile(mile) 
39.37 in = 1 m 
kilometre (km) 

1 yd = 91.44 cm 

12 in = 1 ft 
0.6214 mile = 1 km 
10 mm = 1 cm 
3 ft = 1 yd 
1 mile = 1.6093 km 
100 cm = 1 m 
1760 yd = 1 mile 

1000 m = 1 km 
Area 


Units:square in (sq in; in^{2}) 
1 in^{2} = 6.4516 cm^{2} 
Units: square mm (mm^{2}) 
square ft (sq ft; ft^{2}) 
10.76 ft^{2} = 1 m^{2} 
square cm (cm^{2}) 
square yd (sq yd; yd^{2}) 
1 ft^{2} = 0.0929 m^{2} 
square m (m^{2}) 
square mile (sq mile) 
1.196 yd^{2} = 1 m^{2} 
hectare (ha) 

1 yd^{2} = 0.8361 m^{2} 
square km (km^{2}) 

1 acre = 4046.86 m^{2} 

144 in^{2} = 1 ft^{2} 
2.471 acre = 1 ha 
100 mm^{2} = 1 cm^{2} 
9 ft^{2} = 1 yd^{2} 
0.3861 mile^{2} = 1 km^{2} 
10000 cm^{2} = 1 m^{2} 
4840 yd^{2} = 1 acre 
1 mile^{2} = 2.59 km^{2} 
10000 m^{2} = 1 ha 
640 acre = 1 sq mile 

100 ha = 1 km^{2} 
Volume 


Units: cubic in (cu in; in^{3}) 
1 in^{3} = 16.3871 cm^{3} 
Units: cubic cm (cm^{3}) 
cubic ft (cu ft; ft^{3}) 
1 ft^{3} = 28.3 dm^{3} 
cubic decimetre (dm^{3}) 
cubic yd (cu yd; yd^{3}) 
35.31 ft^{3} = 1 m^{3} 


1.308 yd^{3} = 1 m^{3} 
cubic m (m^{3}) 
1728 in^{3} = 1 ft^{3} 
1 yd^{3} = 0.7646 m^{3} 

27 ft^{3} = 1 yd^{3} 

1000 cm^{3} = 1 dm^{3} 
100 ft^{3} = 1 register ton 
1000 dm^{3} = 1 m^{3} 

Capacity / Volume of Liquids and Gases 


Units: fluid ounce (fl oz) 
1 floz (UK) = 28.4 ml 
Units: millilitre (ml) 
gill (UK gill, US gill) 
0.035 floz = 1 ml 
cubic centimetre 
pint(UKpt, US pt) 
1 gill (UK) = 142 ml 
(cm^{3}, ccm, cc) 
quart(UKqt, USqt) 
1 gill (US)= 118.3 ml 
litre (l) 
gallon(UKgal, USgal) 
1 pt(UK) = 568 ml 
cubic dm (dm^{3}) 

1 pt(US) = 454 ml 
kilo litre (kl) 
5 fl oz = 1 UK gill 
1 qt (UK) = 1136 ml 
cubic metre (m^{3}) 
4 fl oz = 1 US gill 
1 qt (US) = 909 ml 

4 gills = 1 pt (UK,US) 
1 gal (UK) = 4.546 l 
1 ml = 1 cm^{3} 
2 pt = 1 qt (UK,US) 
1 gal(US) =3.7851 
1000 ml = 1 l 
4 qt = 1 gal (UK,US) 
0.22 gal (UK) = 1l 
1l = 1 dm^{3} 
1 UK gal = 1.2 US gal 
0.26 gal (US) = 1l 
10001 = 1 kl = 1 m^{3} 
Mass 


Units: ounce(oz) 
1 oz = 28.3 g 
Units: milligram (mg) 
pound (lb) 
0.035 oz = 1 g 
gram (g) 
stone(stone) 
1 lb = 0.454 kg 
kilogram (kg) 
hundredweight(cwt) 
2.205 lb = 1 kg 
tonne(t) 
ton (ton) 
1 stone = 6.35 kg 


1 UK cwt = 50.8 kg 
1000 mg = 1 g 
16 oz = 1 lb 
0.98 long ton = 1 t 
1000 g = 1 kg 
14 lb = 1 stone 
1 long ton = 1.016 t 
1000 kg = 1 t 
8 stone = 1 UK cwt (long) 
1.1 short ton = 1 t 

112 lb = 1 UK ton (long) 
1 short ton = 0.907 t 

100 lb = 1 US ton (short) 


Density 


Units: lb/cu ft (lb/ft^{3}) 
1 lb/ft^{3} = 16.02 kg/m^{3} 
Unit: kg/m^{3} 

lb/UK gal 
1 lb/Ukgal = 100 kg/m^{3} 

lb/US gal 
1 lb/US gal = 120 kg/m^{3} 
Force 


Units: lbf 
1 lbf = 4.448N 
Units: newton(N) 
tonf 
1 tonf = 99641 Kn 
kilonewton (kN) 
Pressure 


Units: lbf/in^{2} (psi) 
1 lbf/in^{2} = 6895 Pa 
Units: pascal (Pa) 
tonf/ft^{2} 
145 Ibf/in^{2} = 1 Mpa 
megapascal (MPa) 

1 UK tonf/ft^{2} = 0.107 MPa 
newton/mm^{2} 

9.32 UK tonf/ft^{2} = 1 MPa 
(N/mm^{2}) 


bar (bar) 


1 Pa = 1 N/m^{2} 


1 MPa = 1 N/mm^{2} 


1 bar = 0.1 N/mm^{2} 
Energy, Work, Heat 


Unit: British thermal 
1 Btu = 1055 J 
Units: joule(J) 
unit (Btu) 
0.948 Btu = 1 kJ 
kilojoule(kJ) 

1 Btu = 0.000293 kWh 
calorie(cal) 

3413 Btu = 1 kWh 
kilowatt hour (kWh) 


watt second (Ws) 


newton metre (Nm) 


pascal cubic metre 


(Pa m^{3}) 


1 J = 1 Nm = 1 Ws = 1 Pa m^{3} 


1 J = 0.239 cal 


1 kWh = 3600 kJ 
Power, Energy Flow Rate 


Units: Btu/h 
1 Btu/h = 0.293 W 
Units: watt (W) 
ft lbf/s 
3.412 Btu/h = 1 W 
joules/second (J/s) 
horsepower(hp) 
1 ft lbf/s = 1.356 W 
hp metric 

0.74 ft lbf/s = 1 W 

1 hp = 550 ft lbf/s 
1 hp = 745.7 W 
1 W = 1 J/s 
1 hp = 2545 Btu/h 

1 hp metric = 735.5 W 
Thermal Conductivity 


Unit: Btu/ft2h degF 
1 Btu/ft^{2}h deg F = 0.144 W m deg C 
Units: W/m degC 

6.94 Btu/ft^{2}h deg F = 1 W/m deg C 
kcal/m h deg C 

1 Btu/ft^{2}h deg F = 0.124 kcal/m h deg C 


8.06 Btu/ft^{2}h deg F = 1 kcal/m h deg C 
1 W/m deg C = 0.861 kcal/m h deg C 


1 kcal/m h degC = 1.163 W/m deg C 
Velocity 


Units: ft/s 
1 ft/s = 0.305 m/s 
Units: m/s 
miles per hour (mph) 
3.28 ft/s = 1 m/s 
km/h 

1 mph = 1.609 km/in 


0.62 mph = 1 km/in 

MISCELLANEOUS CONVERSION FACTORS
Temperature
Difference of temperature
1 degree on the Centigrade or Celsius scale (deg C)
= 1.8 degrees on the Fahrenheit scale (deg F)
Temperature reading on thermometer
0°C = 32° F (water freezing point)
100°C = 212° F (water boiling point)
Calculation of temperature difference
1 deg C= 9/5 deg F
1 deg F= 5/9 deg C
Calculation of temperature level
0 °C = 5/9x(°F32)
0 °F = 9/5x °C+32
FIGURE
Angles and Slopes
These are mainly required for sloping roofs, which are generally expressed in degrees, but which are difficult for the worker to measure out on the site. Therefore roof slopes are best expressed in simple relations between height and span' preferably using round numbers. Since they are difficult to visualize, the approximate relations between some common slopes (given in ratios and percentages) and angles (in degrees) are shown in the following table:
Ratio of slope 
Percentage of slope 
Angle 
1:50 
2% 
= 1° 
1:25 
4% 
= 2° 
1:20 
5% 
= 3° 
1:10 
10% 
=5.5° 
1:5 
20% 
=11.5° 
1:4 
25% 
=14° 
1:3 
33.3% 
=18.5° 
1:2 
50% 
=26.5° 
2:3 
66.7% 
=33.5° 
3:4 
75% 
=37° 
4:5 
80% 
=38.5° 
1:1 
100% 
=45° 
5:4 
125% 
=51.5° 
4:3 
133.3% 
=53° 
3:2 
150% 
=56.5° 
2:1 
200% 
=63.5° 
3:1 
300% 
=71.5° 
4:1 
400% 
=76° 
5:1 
500% 
=78.5° 
10:1 
1000% 
=84.5° 