Estimate class
A label declaring how mature the scope definition was when an estimate was produced, and therefore how wide its expected accuracy range is.
AACE International classifies cost estimates into five classes. The maturity of the project definition deliverables is the sole primary determinant of the class. Estimating method, purpose and expected accuracy are secondary characteristics that correlate with definition maturity rather than setting it.
The classes run downwards as definition improves. Class 5 is the least defined, produced at nought to two per cent definition for concept screening. Class 1 is the most defined, at sixty-five to one hundred per cent. For building and general construction, a Class 5 estimate carries an expected accuracy range between minus twenty and minus thirty per cent on the low side and plus thirty to plus fifty on the high side, quoted at an eighty per cent confidence interval after contingency.
The ranges differ by industry. AACE publishes separate addenda, and each excludes the sectors covered by the others. The building and general construction addendum does not address transport infrastructure, dams, tunnels, or one-of-a-kind projects such as stadiums, research buildings and health facilities. The process industries addendum excludes commercial building construction and transport infrastructure in turn.
Sources
AACE International Recommended Practice 56R-08, Cost Estimate Classification System as applied in engineering, procurement and construction for the building and general construction industries, revision of 7 August 2020, Table 1. AACE International Recommended Practice 18R-97, the process industries equivalent, 2 February 2005.
Belongs to
Inception & Development
Argued in full
An estimate is a measure of how well the scope is defined