AACE contingency & accuracy range calculator

The AACE classes at a glance

Representative values per AACE International RP 17R-97 / 18R-97 (process industries). The class reflects project definition maturity — not ambition: claiming Class 3 accuracy on Class 5 definition is self-deception, and contingency never covers missing scope.

• Class 5 — 0 to 2 % project definition: accuracy -35% / +65%, contingency 40% (typical range 30–50 %)
• Class 4 — 1 to 15 % project definition: accuracy -22% / +35%, contingency 25% (typical range 20–30 %)
• Class 3 — 10 to 40 % project definition: accuracy -15% / +20%, contingency 15% (typical range 15–20 %)
• Class 2 — 30 to 75 % project definition: accuracy -10% / +15%, contingency 10% (typical range 8–12 %)
• Class 1 — 65 to 100 % project definition: accuracy -5% / +10%, contingency 5% (typical range 3–8 %)

Ranges are indicative midpoints — RP 18R-97 gives wider envelopes depending on technology maturity and complexity.