Sometimes it takes one resource to complete a task, but other times you need more. Sometimes a resource can only work part time. To account for these differences, Microsoft Project uses units to calculate the exact amount of time resources can work on a task.
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What exactly are units?
Units indicate the percentage of a work resource's time that is assigned to a task. There are two types of units in Project: maximum units and assignment units.
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Maximum units When you want to specify how much time a work resource has available for work on all tasks in a project, you specify maximum units in a resource view. This total is used to calculate how much time a work resource can spend on each task assignment.
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Assignment units When you want to specify how much of a work resource's time is dedicated to a specific task, you enter assignment units. You also specify assignment units for material resources to indicate the quantity of material being used for the assignment.
Note: Cost resources, such as airfare or lodging, do not use units because they do not depend on depend on the amount of work performed.
How do I use maximum units for work resources?
Use the Max. Units field in a resource view to indicate whether the work resource is full time or part time on this project, or whether multiples of this resource are consolidated into one. For example:
| If you want to indicate that all a person's time is devoted to your project, type 100% in the Max. Units field on the Resource Sheet view. If the person works 8-hour days, he or she will be overallocated if any combination of assignments exceeds 8 hours (100%) of the available work day. |
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| | If you want to indicate that only a part of a person's time is devoted to your project, type a number less than 100% in the Max. Units field on the Resource Sheet view. If the person works 8-hour days and has 75% of his or her time devoted to your project, her or she will be overallocated if any combination of assignments equals more than 6 hours (75%) of the available work day. |
| | If you want to indicate that a resource group, such as three carpenters, will work on the project full time, type 300% in the Max. Units field on the Resource Sheet view. |
This percentage (the units value) is based on the availability shown in the resource calendar. By default, the resource calendar is the Standard project calendar, which specifies a 40-hour work week. But if you've assigned a different base calendar to a resource or customized the resource calendar the maximum units value is based on that calendar instead. By using a percentage for units instead of an hour value, project and task calculations remain accurate, even if the calendar changes.
How do I use assignment units for work resources?
You can indicate the level of effort for a work resource on a specific assignment in two places:
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In the Resource tab, click on Assign Resources. Enter information in the Units field.
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In the Task tab, click Information and then click the Resources tab. Enter the information in the Units field.
Assignment units indicate how much of the resource's available time, according to the resource calendar, is being used to work on a particular task. For example:
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Specify 100% if the resource is to work full-time on the assignment. This is the default for all assignments.
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Specify 50% if the resource is spending half the available time on this assignment. Even if the resource is a full-time resource, some assignments may require only a part-time effort, leaving the remaining time available for another assignment.
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Specify 300% if three full-time equivalent resources are working on this assignment. You can specify 250% if two full-time resources and one half-time resource are working on this assignment.
This percentage (the units value) is based on the availability shown in the resource calendar. By default, this is the Standard project calendar, which specifies a 40-hour work week. But if you assign a different base calendar to a resource or customize the resource calendar, the assignment units value is based on that calendar instead.
How do I use maximum units for material resources?
The Max. Units field is not available for material resources because material resources are not associated with calendars or other indications of availability. The amount of material used depends on the specific assignment the material is assigned to and is set with the assignment units.
How do I use assignment units for material resources?
For material resources, the Units (or Assignment Units) field indicates the material consumption rate, that is, the number or rate of units of material being used for the assignment. There are two types of material assignment units: fixed and variable.
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Fixed material consumption indicates that regardless of the task duration, the quantity of materials used is the same.
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Variable material consumption indicates that as the task duration changes, the quantity of materials used changes proportionally. Variable consumption is indicated with a time label added to the material label in the Assignment Units field. While fixed consumption of steel might have an assignment units value in tons, variable consumption might have an assignment units value in tons/day or tons/d. Time labels and abbreviations are indicated the same as other durations: in minutes, hours, days, weeks, or months.
For example, if the assignment units value for steel is 80 tons on a 2-day task, the total consumption (or the material work value) for steel is 80 tons. However, if the assignment units value for steel is 80 tons/day on a 2-day task, the total consumption is 160 tons.
Note: While assignment units for work resources can be expressed as percentages or decimals, material resource consumption rates are always expressed as decimals.
What are peak units?
Peak units are the highest level at which a resource is scheduled for all assigned tasks during a given period of time. Like maximum units, peak units are expressed as percentages or decimals for work resources. For material resources, peak units are expressed as a decimal together with the material label (for example, 40 tons/week).
Reviewing peak units can help you determine whether a work resource is underallocated or overallocated during a certain period of time.
For material resources, you can compare the peak units (the largest consumption rate needed during a certain period of time) with the rate at which the supplier can deliver the material.
Add the Peak field to the table part of the Resource Usage view to see the total peak units for the resource for all assigned tasks. Add the Peak Units field to the timesheet part of the Resource Usage view to see peak units for the selected timescale. You can also see peak units in the Resource Graph view.
How do assignment units and calendars affect the schedule?
For material resources, variable assignment units can affect the schedule. Variable material consumption indicates that as the task duration changes, the quantity of materials used changes proportionally. Likewise, if only variable material resources are assigned to a task, and if you change quantity, the task duration can change accordingly. Variable consumption is indicated with a time label added to the material label in the Assignment Units field. While a fixed consumption of steel might have an assignment units value in tons, variable consumption might have an assignment units value as tons/day or tons/d.
For work resources, task schedules can also expand or contract based on the working time calendars of assigned work resources. Use the project calendar to set the standard working and nonworking times and days for all resources in the project. Use a resource calendar to set exceptions to working times (such as days off or vacations) for individual resources. To access the project and resource calendars, click Change Working Time on the Tools menu and then select the appropriate calendar from the For calendar list.
Resource calendars and assignment units interact to determine assignment scheduling. For example, if Betty's resource calendar is set for 8 hours of working time on Thursdays, and she's scheduled 100% on a task for Thursday, this equates to 8 hours. However, if Betty's resource calendar is set for 4 hours on Friday, and she's scheduled 100% on a task for Friday, she is scheduled to work for 4 hours.
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