There are five different types of cost estimate
| Estimate Type | Probable Error | Purpose | Level of Eng'g Req'd | Cost of Estimate (as % of Total Project Cost) |
|---|---|---|---|---|
| Order-of-Magnitude | -40% to +40% | Feasibility study | None | 0 to 0.1% |
| Study | -30% to +30% | Project evaluation | Preliminary flowsheets, Main equipment sized | 0.1 to 0.2% |
| Preliminary | -20% to +20% | Budget authorisation | PIDs, mass and energy balances, equipment list, equipment specs and data sheets,site layouts incl buildings, project program, engineering manhour estimate | 0.4 to 0.8% |
| Definitive | -10% to +10% | Project cost control | Substantial, but incomplete engineering | 1 to 3% |
| Detailed | -5% to +5% | Contractors' tender | Complete project engineering | 5 to 10% |