Rectangular Sections

The torsion constant J is given by

where is a constant depending on the ratio of , which can be read either from the table below. Linear interpolation may be used for intermediate values.

1.0	0.141		1.5	0.196		2.8	0.258		10.0	0.312
1.1	0.154		1.8	0.216		3.0	0.263		∞	0.333
1.2	0.166		2.0	0.229		4.0	0.281
1.3	0.175		2.3	0.242		5.0	0.291
1.4	0.186		2.5	0.249		7.5	0.305

or from the graph

Note that K converges to 1⁄3 for narrow rectangles.

Alternatively

generally, or if then

and so