For many people who build or buy a house, size counts. The average new house in 1995 had 2,095 square feet, up 575 square feet from 20 years ago, according to the National Association of Home Builders.

But what exactly do those numbers mean? Are they "finished" square feet? Above-ground square feet? Does the figure include stair treads? Closets? Bay windows? Are they measured inside or outside?Whether or not people know what the numbers mean, they are prone to describe their houses in terms of its size, rather than other characteristics. Maybe that's because many people associate size with cost - a passive, subtle way of bragging.

The fallacy here is that the size of the house isn't necessarily an indication of quality or cost. A 10,000-square-foot stick-frame house overlooking a six-lane interstate could cost less than a 1,200-square-foot masonry house with inlaid teak floors, 18-karat gold fixtures and views of the Mississippi.

Many homebuyers don't understand how square footage is determined and what it does - and doesn't - include. But there are some legitimate reasons - beyond bragging rights - why precise square footage is important.

Appraisers, real estate agents, architects, city planners, lenders and others all rely on such figures to market, price and plan a house. But for as many reasons why square footage is important, there are that many ways to determine it.

For years, there was no nationwide standard for measuring square footage in single-family houses. To fill that void, the American National Standards Institute (ANSI) developed and adopted in 1996 a voluntary methodology for measuring square footage in houses. ANSI is a group of professionals including builders, architects and real estate agents.

The new standard says that finished square footage is the sum of finished areas measured at floor level at the exterior finished surface of the outside walls. The figures must be reported as above-grade space and below-grade space.

Architects are front-liners in the square-footage question. Yet for many of them, it's discouraging when prospective clients call to say that they want to build a house with "x number of square feet," says Peter Rand, executive vice president of the Minnesota chapter of the American Institute of Architects. The first considerations should be price and features, he says. After that, talk square footage.

"In a sense, square footage means virtually nothing," Rand says. Buyers "want something to hang their hat on. What people need to hang their hat on is money. . . . I tell them to start from a cost perspective."

Nonetheless, the American Institute of Architects lists the various methods of calculating the area and volume of a building, and it explicitly says that there is no single measurement standard, although they offer guidelines.

To determine "architectural area," the guidelines say, you measure from the exterior face of exterior walls or, in the case of townhouses or other attached units, from the center line of walls separating buildings. Such areas include basements, mezzanines and other similar areas, provided that they have a minimum of seven feet of headroom. It does not include utility recesses, exterior terraces, exterior steps or eaves.

When it comes to selecting a builder, Alan and Denise Fields, authors of "Your New House" (Windsor Peake Press, 1996), say buyers must be careful in making comparisons.

One of the biggest potential mistakes you can make in search for a builder is to shop by the price per square-foot, the Fieldses say. They call it the "square-foot price myth." For example, a builder who says that he will build you a 2,000-square-foot house for $160,000 ($80 a square foot) isn't necessarily giving you a better deal than a builder who will charge you $200,000 for a 2,000-square-foot house ($100 a square foot). Lots of variables, such as quality of materials and construction, amenities and what's included in the quoted measurements, can be concealed in those generalities.

The Fieldses also note that location is an important factor in the square-foot pricing question and that building up (adding a second or third story) is less expensive than building out, thereby reducing the square-foot cost.

These are both reasons why it's dangerous to compare the cost of new homes based only on square footage.

The square-foot factor comes into play for buyers of existing homes, too, because most people want the most space for their money. But that bigger-is-better myth can be quickly dispelled once you visit a property and discover its condition.

Increasingly, when houses are listed with regional Multiple Listing Services (RMLS), there are several square-footage distinctions that are made in an effort to give buyers comparable information.

When a house is listed with the Minneapolis RMLS, several measurements are noted, including foundation size, above-ground finished square feet and below-ground finished square feet. The sum of the above- and below-ground finished square feet equals the total finished square feet.

Even if you're not buying or selling, there still may be reasons why you should be concerned about how the square footage of your house or lot was determined: Such measurements, for example, are the basis for your tax bill, says Gauvin.