Abstract: A vacuum ionization gauging tube, particularly a Bayard-Alpert (B-A) type vacuum ionization gauging tube, has a firmly compact construction, and provides the capabilities for minimizing outgassing gases and measuring pressures accurately without affecting the ultimate pressure range. The B-A vacuum ionization gauging tube includes a filament having a total surface area of between 6 mm.sup.2 and 20 mm.sup.2, a grid formed like a coil from a 0.1 mm to 0.3 mm diameter metal wire, the coil having a diameter of 5 mm to 7 mm and a length of 15 mm to 20 mm and across which it can be energized, an ion collector electrode having substantially the same length as the filament, and a metal envelope for enclosing the above electrode elements and which is maintained at a potential lower than that of the filament. The grid coil has a winding pitch of between 1.5 mm and 2.5 mm. The filament and grid are spaced apart from each other by the distance of between 2 mm and 4 mm.