Units of measurement

Every quantity in an estimate or bill must be measured in a clear, agreed unit, or the contractor and client will argue about what was meant and how much was done. Standard methods of measurement fix the unit, the rules for what is included and deducted, and the precision for each type of work, so that bills from different estimators can be compared and paid fairly.

Typical units follow the nature of the work. Earthwork in excavation and filling is measured in cubic metres. Concrete and masonry are also in cubic metres, while thin items such as plaster, flooring, painting and formwork are in square metres. Linear items such as skirting, pipes, kerbs, railings and fencing are in running metres. Reinforcement and structural steel are by weight in kilograms or tonnes. Doors, windows, fixtures, manholes and fittings are counted in numbers. Lump sums are used only where measurement is impractical.

Measurement rules state, for example, whether openings in walls are deducted (small ones usually are not), how laps in reinforcement are treated, whether work in foundations is measured separately from superstructure, and whether working space or slopes in excavation are included. Dimensions are taken to a stated precision, usually to the nearest centimetre for linear dimensions and to two decimal places for areas and volumes. In India IS 1200 sets these rules part by part for each trade; public works departments add their own schedule descriptions and item units.