A labour constant is the standard time taken by an operative or gang to complete one unit of work, usually expressed in hours per unit, for example hours per m² of painting or per m³ of excavation. Its inverse is the output rate: if a painter can apply 12 m² of paint per hour, the labour constant is about 0.08 hours per m².
Estimators and QSs use labour constants to build up the labour element of a unit rate: the constant multiplied by the all-in labour rate gives the labour cost per unit. Constants come from published price books, work study or, most reliably, a contractor’s own records of past performance, and should be adjusted for the conditions on the particular job, such as access, height, quantity and weather. The QS also uses them to check that tender rates are reasonable and to value variations and disruption claims.
Related terms: Output Rate, All-in Labour Rate, Man Hour Rate, Unit Rate.
