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AACE Estimate Classification: Tool

AACE Estimate Accuracy Range Calculator

Enter an estimate, choose its class, and see the range the final cost is likely to fall within, using the accuracy bands AACE International publishes for each class.

Updated 2 October 2026

Estimate class share of project defined
Not sure which class? Use the class finder
Well understood, low riskComplex, high risk

Class 3 · 80% confidence

Likely low (about P10)
$21.3M

15% below your estimate

Your estimate
$25M

Including contingency

Likely high (about P90)
$30M

20% above your estimate

There is roughly an 80% chance the final cost lands between $21.3M and $30M.

The cone of uncertainty
Select a class to apply it
  • Full published range for the class
  • Where your project sits
  • Your estimate
Show the numbers for every class
ClassLowHigh80% confidence range
Class Finder

Which Class Is My Estimate?

Answer four questions about what exists today. AACE classes an estimate by the maturity of its deliverables, and the least mature deliverable that materially affects cost decides the class.

1How far has the design progressed?
2What do you know about the site?
3How were the quantities produced?
4Where are approvals, land and procurement?
The Published Bands

AACE Accuracy Ranges by Class

Typical variation in the low and high ranges at an 80% confidence interval, from RP 18R-97 (process industries) and RP 98R-18 (road and rail), which publish identical bands.

ClassProject definitionLow sideHigh side
Class 50% to 2%−20% to −50%+30% to +100%
Class 41% to 15%−15% to −30%+20% to +50%
Class 310% to 40%−10% to −20%+10% to +30%
Class 230% to 75%−5% to −15%+5% to +20%
Class 165% to 100%−3% to −10%+3% to +15%
Read This First

How to Use These Ranges Properly

  • The class comes from the deliverables, not the dollar figure. Decide the class from the maturity of the design, survey, geotechnical and other key deliverables. If they are uneven, use the weakest one that materially affects cost.
  • The ranges assume contingency is already included. Apply them to the estimate with contingency, not to the base estimate.
  • They are typical outcomes, not targets. AACE expects the range for a specific estimate to come from a quantitative risk analysis, such as Monte Carlo simulation, which also gives the P50 and P90 values funders ask for.
  • Unusual risks widen the range. Volatile markets, political or stakeholder uncertainty and difficult ground can push outcomes beyond the published bands.

Related: the estimate classification system, P50 and P90 explained, and the Monte Carlo method.

FAQ

Frequently Asked Questions

How do I calculate the accuracy range of an AACE estimate?

Multiply the estimate (including contingency) by one plus the low and high percentages for its class. For a Class 3 estimate of $25 million at the wide end of the band (-20% / +30%), the 80% confidence range is $20 million to $32.5 million. AACE recommends deriving the actual range for a specific estimate from a quantitative risk analysis.

Why are AACE accuracy ranges asymmetric?

Because capital projects are far more likely to overrun than underrun. The high side of every band is larger than the low side, and the difference grows as project definition falls.

Do the accuracy ranges include contingency?

Yes. The published ranges assume the estimate already includes an appropriate contingency. Without contingency the range would be wider and shifted upward.

Are the ranges different for road and rail projects?

No. RP 98R-18 for road and rail publishes the same accuracy bands as RP 18R-97 for the process industries. What differs is how each class is prepared, for example cost per kilometre at Class 5 and Class 4.

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