First, find the estimated/budgeted Man Hours for spot footings. (460man-hours)
Next, schedule duration for this activity, in this example there is 7 working days to complete the spot footing activity.
Now, take man-hours and divide by days - 460/7= 65
So you have 65 man-hours a day for a seven day duration to complete the footings.
Then you want to determine your crew size based of your daily man-hours
First take the daily hours 65 and divide by the crew size you would like to have, let's try 10 men. 65/10=6.5 if you have ten guys to stay in budget you could only work on spot footings for 6.5 hours a day, if you have 10 men for 8 hours a day for 7 days.- your total man-hours would be 560 (100 hours over budget)
Let's try a crew size of 8.
65/8.1= 8 so you could have a crew of 8 for eight hours a day for seven days- your total man-hours would be 448 (12 hours under budget).
There are many factors that come into play when determining crew size and it's easy to get over-whelmed. You have to break apart each task, understand the job flow, sequencing and schedule. But if you start with one task and work all the way through it then move to the next task and so forth, you start to create the data needed for an average crew. Maybe you only need 8 on spot footings but 10 on walls and four on columns, after you know your crew size you can double back to the schedule and see if the sequencing works out where you can get away with a crew size of 14 because of all the trade work or down time in-between activities or on pour days. The more you practice the easier it becomes.
The important part is that you learn and understand hours/cost on every activity you are part of, and it's never to late to start. In the case that you are not shown the budget or hours by your Foreman or Supervisor click here for a MH/Unit form that you can start tracking yourself. You want to become great at what you do, so empower yourself to learn, grow and excel above those who don't want to share the information.