In order to obtain the practical vacuum data in field emission display packages which are composed of very thin gapped glass plates, the effects of heating time and temperature as well as geometrical factors such as the gap size between the glass plates, the inner;diameter, and length of the evacuation tube were investigated. Even though the evacuation system is in an ultrahigh vacuum of more than 1.0x10(-7) Torr, the attained vacuum level with 55 mmX55 mmX1.1 mm panel was 3.0 x 10(-5) Torr. The attainable vacuum level for the panel was calculated by considering conductance of the evacuation system. The calculated and measured values are consistent (2.8X10(-5) and 3.0 X 10(-5) Torr). Heating glass frit sealed packages do not improve vacuum level and H, H2O, CO, and CO2 were identified as impurities remaining inside of the panels.