Abstract: A process and apparatus is provided for measuring the volume of workpiece spaces, especially combustion chamber spaces in cylinder heads for internal combustion engines. Pressurized air is supplied to the workpiece space and the pressure compared with the pressure in a similarly supplied known control volume. To compensate for temperature differences in respective workpieces being tested, a second temperature correcting pressurized air circuit is provided which includes a test chamber space in a part attachable directly to the workpiece surface. This test chamber part thus experiences the workpiece temperature and a temperature compensating signal is generated and processed to correct the volume indicating signal.