Methods for Estimating Time

Methods for Estimating Time

We'll now look at different approaches that we can use to estimate time. We'll probably find it most useful to use a mixture of these techniques.

• Bottom-Up Estimating
• Bottom-up estimating allows us to create an estimate for the project as a whole. To analyze from the "bottom up," break larger tasks down into detailed tasks, and then estimate the time needed to complete each one.
• Because we're considering each task incrementally, our estimate of the time required for each task is likely to be more accurate. We can then add up the total amount of time needed to complete the plan.

Top-Down Estimating

• In top-down analysis, we develop an overview of the expected timeline first, using past projects or previous experience as a guide.
• It's often helpful to compare top-down estimates against our bottom-up estimates, to ensure accuracy.

Comparative Estimating

• With comparative estimating, we look at the time it took to do similar tasks, on other projects.

Parametric Estimating

• With this method, we estimate the time required for one deliverable; and then multiply it by the number of deliverables required.
• For example, if we need to create pages for a website, we'd estimate how much time it would take to do one page, and we'd then multiply this time by the total number of pages to be produced.

Three-Point Estimating

• To build in a cushion for uncertainty, we can do three estimates - one for the best case, another for the worst case, and a final one for the most likely case.
• Although this approach requires additional effort to create three separate estimates, it allows us to set more reasonable expectations, based on a more realistic estimate of outcomes.

Man-hour Estimation

One “man-hour” is one hour of one worker. If one worker can pour one 1 m3 concrete in 15 hours, then 1 m3 can poured in 15 man-hours. Theoretically, with three workers working, one m3 conrete can be poured in five hours.
Spent Man-hour
Spent man-hour is the actual man-hour spent on site during the execution of any given activity.
Planned Unit Man-hour
 “Planned unit man hour” is defined at the beginning of the Project, and provides the man-hours required to perform of one unit of any given activity.
 Earned Man-hour
Earned man-hour the result of the formula where the actual installed quantity for any given time period for any given activity is multiplied by Planned Unit Man-hour. The Earned is used for progress calculations and shows the man-hour that would have been spent to install the “actual quantities” if the planned unit man-hour would have been the same as spent man-hour. Unit planned man-hour and site actual quantities are needed for calculation.
Planned Man-hour
Planned man-hour is the total man-hour for any given activity and it is the result of the multiplication of Planned Unit Man-hour by total quantity. If there is 10000 m3 concrete to be poured at the project, then the planned man-hour is 15 man-hours / m3, then planned man-hour for concrete works are 150.000 man-hours.;

Formula for Man hour calculation:

MDH/W = Constant

Where,

M = number of men
D = number of days
H = number of hours per day
W = amount of work

Estimating the number of man-hours required to do a task is often the core issue in most projects.
While it may not represent the largest number in sheer dollars, particularly if it is a capital project, it is the one that is the most widely variable, and will have the most long-term impact in functionality, we are going R&M costs, reliability, and getting finished project price as completed as close to the bottom line estimated as possible.

There are 2 aspects to the question we are asking: how many man-hours will the project take, and what are the components of calculating the rate.

Often man-hour estimates are most accurate when done by an expert. One should never rely on the client's estimation of how long any task will take. As the project manager get our own experts to offer an opinion. Do not forget to include not only those who are directly working on the project, but any temporary workers who may have to be hired either to work directly on the project or to replace the workers who are being moved onto the project. Additionally, don't forget to account for administrative personnel, business office personnel, and executive oversight.

We will want to figure in an error factor, which will vary depending on how complex the project is, whether our personnel are experienced at this type of work, whether there are any weather dependent variables, and whether our subcontractors are people we have worked work with and we can trust their delivery estimates .In most cases, even if the project is something with which we have experience, we add approximately 15 to 25% to the man-hour estimates. While the point of budgeting is to be accurate, it is always better to err on coming in under budget rather than over. We'll probably have a wrestling match with our salesman who is presenting the bid over this issue. Stick to our guns, a reputation is built on long-term trust and repeat business from a customer. A customer always feels better about paying less than we estimated.

Depending on the size of the project, it may be useful to come up with an average hourly rate or classes of hourly rate if there is a wide disparity between the skill levels and pay levels of participants. For example, we may have an executive rate, managerial rate, skilled technician rate, and general labor rates classifications and break down our estimates of man-hours by class. This will give us a better estimate in terms of its accuracy, and is certainly more efficient in large-scale projects than trying to run every employees information. On a small project were there a few employees, or where the pay scale is fairly uniform among employees, a single average rate will do.