A versatile system for measuring the thermal expansion and the magnetostriction of spherical samples has been developed. A diaphragm sensor was constructed for measuring changes in strain (&Dgr;l/l0) in the range 10−3–10−6. A strain gauge technique is used where the change in length of the sample is determined by measuring the deformation of a membrane. A linear correlation between the change of length and the output signal of the sensor is shown. The temperature dependent calibration function is determined by a data processing system. The device is calibrated by using the known thermal expansion of Ni and Al in the temperature range 80–300 K. The correct operation of this technique is verified by measuring the thermal expansion of Cu and Nb. In addition the thermal expansion of Tb, Dy, TbCo2, and DyCo2have been obtained and the results are in good agreement with published data.