Figuring out how much of something you will need for a given project can be confusing.

It might be easy to figure out the area of a room is by calculating length times width, but what about determining how many rolls of wallpaper will be needed? Let's see: length times width of the room, converted to inches and divided by the width of the wallpaper times the length of the roll divided by 12 . . . you get the point.

Why not use a calculator? Well, using a calculator can be one solution if you know how to accurately convert fractions of an inch to their decimal equivalents.

Now there is a really simple solution to all this calculating mumbo jumbo. It is a new breed of calculator -- the "fractional" calculator made especially for builders and remodelers. We used to call them "foot-inches" calculators. Fractional calculators add, subtract, multiply and divide fractions. You can actually add 35/8 inches together with 21/4 inches and get the right answer -- 57/8 inches.

However, builder and construction calculators are fractional calculators that take the next step.

Here is an example of a common problem associated with using a standard calculator to acquire a measurement value: Spacing the spindles in a homemade handrail system is easy. All you have to do is divide the overall length of the rail by an estimated number of spindles until you get an answer that approximates your spacing need -- not too wide, not too narrow. Sounds simple until you have to make the measurement with a decimal answer. Did you ever try finding 0.33333 inches on a measuring tape? Good luck!

On the other hand, with a standard fractional calculator, you enter the overall length of the rail in feet and inches, fraction of an inch included, and divide by the approximate number of spindles desired. The answer that is fed back can be found on any measuring tape.

Building and remodeling fractional calculators take construction calculations to a new level of ease and simplicity. These units enlist dedicated function keys to make construction-specific calculations that would otherwise be difficult to perform on any kind of calculator, including the most sophisticated of fractional calculators.

At the press of a button, one can figure how many rolls of wallpaper or how many yards of carpet will be needed. And the most common calculation of all: how many gallons of paint to buy. All are light work when using the dedicated function keys on a home-improvement fractional calculator.

When shopping for a construction calculator, there are a few things you need to know. First, most experts agree that the less expensive models (less than $25) are best suited for the do-it-yourselfer. They have fewer functions and features, making them less complex to use.

Next, compare functions. Among the various features that are available:

* Basic math keys

* Fractional keys

* Board-foot key

* 4x8 sheet stock key

* Paperless tape

* Fixed fraction mode

* Triangle keys

* Circle/arc keys

Each calculator offers some, but probably not all, of the above features. Choose the ones that are most important to you before taking the dive.

By the way, you may have some difficulty finding these babies on the Web. There doesn't seem to be any one category that you can type into a search engine that will give you a list of all the various units that are available.

You can type in "fractional calculator," but you may not come up with one that is construction specific. It depends on which search engine you use.

Here are Web sites for several companies that make the various units and the part numbers that will have to be used to find the item within that site:

*, part 8525

*, part 104642 or part 949811

*, part 39749 or part 39785

*, part 86K78.07 or part 86K78.10