When to use bar chart, CPM, PERT

The method is chosen according to the size of the project, nature of the activities and the certainty of the time estimates.

Bar chart

Use it when:

• the project is small, simple or has few activities (a house, a small culvert);
• a quick, easy-to-read schedule is needed for site staff or for a presentation to top management;
• the work is at the preliminary stage and the logic is not yet detailed;
• progress is to be shown to people without technical training.

CPM (Critical Path Method)

Use it when:

• the project is large and complex, with many inter-related activities, but the durations can be estimated with fair certainty from experience (roads, buildings, bridges, canals);
• the critical path and floats are needed;
• time-cost trade-off (crashing) and resource scheduling are required;
• the project is repetitive or similar projects were done before.

PERT (Programme Evaluation and Review Technique)

Use it when:

• the work is new, research-type or has no past data (first-of-its-kind hydropower, tunnelling, software, defence projects);
• activity durations are uncertain and three estimates (optimistic, most likely, pessimistic) are needed;
• the probability of finishing the project by a given date is to be found;
• the main interest is time, not cost.