Parametric estimating, a more accurate technique for estimating cost and duration, uses the relationship between variables to calculate the cost or duration.
Essentially, a parametric estimate is determined by identifying the unit cost or duration and the number of units required for the project or activity.
The measurement must be scalable in order to be accurate.
For example, if it took me two hours to mow my one acre yard last week and this week I’m mowing four acres, I could estimate that it will take eight hours to mow.
However, if the first one hour was spent transporting my tractor and preparing it to mow, the estimate would need to be scaled appropriately: 1 hour for transporting and then four hours to mow, for a total of five hours.