Work is said to be done by or against a force, when its points of application moves in a or opposite to the direction of the force and is measured by the product of the force and the displacement of the point of application in the direction of force.

i.e.  Work done, W = Force [F]x distance [d]
The S I or M.K.S. unit of work is the joule, which is defined as the work done when a force of one newton acts through a distance of one metr in the direction of the force. Hence if a force F acts through distance d in its own direction.

W = F [newtons] x d [metres] = Fd joules

The units of work in F.P.S and C.G.S. systems are foot-poundal and ergs respectively.

The gravitational units of work are ft.-Ib, gram-cm and kg-m where
1 ft-Ib = 32.2 ft-podndals
1 gm-cm = 981 dyre-cm
1 kgf-m = 9.81 Newton-metres
Relation between joule. Erg, ft-poundul, kgf.m. gm-cm and foot-pound.
1 joule = 1 N-m = 105 dynes x 100 cm =107 dyne-cms or ergs
1 Foot-poundal = 13,825 dynes x 30.48 cm = 21,400 ergs or 0.04214 joules
1 Fo t-pound = 32.2 ft-poundals = 32.2 x 4, 21,400 = 1.36 x 107 ergs or 1.36 joules

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