The conservation and preservation of heritage historical masonry buildings requires the evaluation of their structural capacity against gravity and horizontal actions. This evaluation is normally based on meaningful mechanical properties such as the masonry compressive strength. The compressive strength of masonry is highly dependent on the compressive strength of the components. Specifically the experimental assessment of compressive strength in solid fired clay bricks has long been a topic of debate, with various standards describing different specimen shapes, sizes and bearing surfaces treatment. There is an evident lack of consensus on common criteria and procedures for brick mechanical testing. This research focuses on evaluating the compressive strength of two types of solid clay bricks, corresponding to mechanically extruded ones and traditionally handmade bricks by moulding. The reference standards considered are the American ASTM C67, the European EN 772–1, the Australian AS/NZS 4456:4, and the Canadian CAN/CSA A82. These standards encompass different specimen shapes, such as whole or half bricks and 100 × 100 × 40 mm3 specimens subjected to various bearing surface treatments, including grinding, capping with cement mortar or gypsum plaster, and placing with birch plywood or fiberboard. Additionally, a novel bearing surface treatment involving the placement of two oiled PTFE sheets on each specimen loading surface is proposed. The experimental campaign focuses on evaluating the compressive strength based on a comparison of the results obtained using the reference standards. The results highlight and quantify the variations in compressive strength obtained for the same type of solid fired clay brick when different reference standards are considered. In addition, the results reveal the potential of using PTFE sheets as a promising possibility for brick mechanical characterization. The PTFE sheets cause very low friction at the specimen-platen surface and therefore allow the measurement of strength values not influenced by the specimen shape.