Accuracy of Estimates

[IronMike]

Are there some rules of thumb for accuracy of estimates at various stages of engineering, like ballpark, back of envelope, preliminary engineering, detailed engineering, etc? Seems like I have seen figures from 250% going down to 10% as engineering effort is expended.

 

[mohtogh]

Hi,
Type of cost estimation Usual reliability
1. Order -of-magnitude + ,- 30 to 60 %
2. Study + , - 30%
3. Preliminary + , - 20%
4. Definitive project control + , - 10%
5. Detailed estimate + , - 5%

As you know , we have 5 standard cost estimation.
Hope this help