The performance of powertrain components and rock tools relies on the inherent strength and hardness of ferrous martensite. Currently the industry uses experimental measurements of surface hardness and case depth to qualify their hardening processes. Often there are additional requirements on microstructure constituents, although there are no quantitative methods available to characterize ferrous martensite. Here such methodology is discussed in relation to EBSD measurements on the full practical range of Fe-C alloys. The orientation relationships between austenite and martensite along with the variant pairing tendency of martensite are determined from the EBSD data. These results are related to the well-known morphological transition from lath to plate martensite in Fe-C alloys. Quantitative metallography using EBSD has the potential to complement hardness- and residual-stress measurements when qualifying new steel grades and hardening processes in industry. It may also prove important when investigating the coupling between material properties and fatigue performance.