How to use the COCOMO Model Calculator
- 1. Enter size and modeType the size in KLOC and pick organic, semi-detached or embedded.
- 2. Choose the modelUse Basic COCOMO, or Intermediate to rate the 15 cost drivers.
- 3. Read the estimateSee effort, development time, average staff and productivity, with every formula shown.
COCOMO 81 formulas
Boehm's Constructive Cost Model (COCOMO 81) estimates effort from size in thousands of lines of code (KLOC).
- Effort E = a × KLOCb person-months (× EAF in Intermediate COCOMO).
- Development time D = c × Ed months.
- Average staff = E ÷ D, and productivity = KLOC ÷ E.
Basic constants: organic a = 2.4, b = 1.05; semi-detached a = 3.0, b = 1.12; embedded a = 3.6, b = 1.20. For time, c = 2.5 in all modes, with d = 0.38, 0.35 and 0.32. Intermediate COCOMO uses a = 3.2, 3.0 and 2.8 and multiplies by the effort adjustment factor (EAF). EAF is the product of 15 cost-driver multipliers such as RELY, CPLX, ACAP and TOOL.
Worked example
An organic project of 32 KLOC with Basic COCOMO:
- E = 2.4 × 321.05 = 2.4 × 38.05 ≈ 91.3 person-months.
- D = 2.5 × 91.30.38 ≈ 13.9 months.
- Average staff = 91.3 ÷ 13.9 ≈ 6.6 people.
A 400 KLOC embedded project gives E = 3.6 × 4001.2 ≈ 4,773 PM and D ≈ 37.6 months. The b exponent is above 1, so effort grows faster than size.
Choosing the mode
Organic: a small team on a familiar, flexible project, such as a payroll system. Semi-detached: a mixed team with medium experience, such as a database or compiler. Embedded: tight hardware, real-time or regulatory limits, such as flight control. Results are textbook estimates for study, not quotes. Testing effort can be estimated with the test estimation calculator. For size in function points instead of KLOC, use the function point calculator.
Frequently asked questions
What is a person-month?
The work one person does in one month. 91 PM could be about 7 people for 13 months.
When should I use Intermediate COCOMO?
When the question gives cost-driver ratings such as high reliability or very high analyst capability. Otherwise Basic COCOMO is expected.
Is this COCOMO II?
No. This is COCOMO 81 (Basic and Intermediate), the version in most university syllabi. COCOMO II uses scale factors and different constants.
How is cost worked out?
Effort in person-months × your cost per person-month. Enter your own rate, because salaries vary.