This website is a design guide to BS 5950: Part 1 now denoted as BS 59501: 2000^{[1]}. The symbols used are generally the same as those in BS 59501: 2000.
1.1 Material, section dimensions and tolerances
The structural sections referred to in this design guide are of weldable structural steels conforming to the relevant British Standards given in the table below:
Table – Structural steel products
1.2 Dimensional units
The dimensions of sections are given in millimetres (mm).
1.3 Property units
Generally, the centimetre (cm) is used for the calculated properties but for surface areas and for the warping constant (H), the metre (m) and the decimetre (dm) respectively are used.
Note: 
1 dm 
= 0.1 m 
= 100 mm 

1 dm^{6} 
= 1 x 10^{–6} m^{6} 
= 1 x 10^{12} mm^{6} 
1.4 Mass and force units
The units used are the kilogram (kg), the Newton (N) and the metre per second (m/s^{2}) so that 1 N = 1 kg x 1 m/s^{2}. For convenience, a standard value of the acceleration due to gravity has been generally accepted as 9.80665 m/s^{2}. Thus, the force exerted by 1 kg under the action of gravity is 9.80665 N and the force exerted by 1 tonne (1000 kg) is 9.80665 kilonewtons (kN).