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In domestic, the determination for thickness of fire protection materials of steel column has been conducted by using of one size of steel column, H-300x300x10x15, since the early 1990's with the critical temperature, 350℃ as a performance criterion. But there have been something problems when the thicknesses of fire protection materials that were chosen through fire tests for getting an approval from fire authorities was used to a real structural column. One is that some columns are needed overprotected, which is inclined to leading much cost of construction and resulting in less effectiveness in contrast to concrete based construction, the other is that there is absent of fire safety of building where in deed the fire protection material is needed more than that approved from fire tests. To make the new determination method of thickness for fire boards covered at steel columns, we utilized a new process including a section factor and the new criterion of performance of fire resistance for the small specimens in 1 meter covered fire boards that was chosen between a critical temperature from life-size loaded column in 3.5 meters and that being defined at KS F 2257-7 in 538℃. To demonstrate and make a new equation for determination of thickness of fire board, we carried out 4 times fire test with full-size specimens and 8 times with small-size specimen consisted of H-sections and square rectangular sections, respectively. With several fire test data, we can derived a FR = 63.25 - 0.24Hp/A + 2.76t (R=0.99) for a gypsum board and FR= 41.30 - 0.1Hp/A + 2.52t(where FR: Fire resistance(mins), Hp: Heated parameter, A :Area of Section, t: thickness of fire material(mm)) for a CRC board, respectively.