P6 Activity Duration Calculator

In Primavera P6, each activity needs an original duration. Guessing durations leads to unrealistic schedules; deriving them from quantities and production rates makes the schedule defensible and easy to update. This calculator converts a quantity of work, a crew's daily output and the number of crews into an activity duration in working days.

How to use it

1. Enter the work quantity from the BOQ or take-off, such as 450 m² of formwork.
2. Enter the production rate of one crew per day, such as 30 m² per crew-day.
3. Enter the number of crews and, optionally, working hours per day.
4. Read the duration and round it to whole days for P6.

The formula

Duration (days) = Quantity / (Output per crew per day × Number of crews)

Worked example

Blockwork of 1,200 m², one crew of 2 masons and 2 helpers produces 20 m² per day. With 3 crews: 1,200 / (20 × 3) = 20 working days. With 2 crews it becomes 30 days, which shows the trade-off between resources and time.

Making durations realistic

• Use proven production rates from your company's historical data or recognised norms, adjusted for site conditions.
• Apply efficiency factors for weather, height, congestion and learning curve, often 0.7 to 0.9.
• Respect crew limits: adding crews only helps if there is enough workspace; doubling crews rarely halves the duration on a congested floor.
• Match the calendar: P6 durations are in working days of the activity's calendar, so a 6-day week calendar finishes sooner in calendar time than a 5-day one.
• Record the quantity and rate in activity notes or user-defined fields so the logic can be audited.