The increase of urban built-up area is propelled by many factors of society,economy and urban environment.

We start at the rank-size rule by urban population and the rank-size rule by urban built-up area, and derive a mathematical relationship that the land use size of a city and its population .

So construction area calculating methods could not exchange, which should be paid attention especially of the project estimation, between construction and real estate industry.

In order to improve the accuracy of house construction cost budgetary estimate during the feasibility research, the unitary linearity regress method is used to study the linearity relationship between project amount and construction area.

This paper introduces the concepts and functions of the floor area,and makes the comparison of the new standard and old regulation in calculating the floor area of the building works.

The floor area ratio for every grid cell has been computed through the analysis of the linear relationship between the percent of the building shadows area from building land and the floor area ratio in investigating grid cell.

Building size, floor area and other factors should be taken into account.

Measure of building area s comparison between new norm and past rules;

Suitable building area, gas price, cost of gas air conditioner set and heat prices of centralized heat-supply for gas air-conditioning system were obtained in order to choose gas air-conditioner or electric air-conditioner.