The agricultural sector contributes 9% towards total UK greenhouse gas emissions and so may offer significant potential as a sector to help meet national and international emission reduction targets. In order to help farmers manage their emissions and to encourage more sustainable farming, several carbon accounting tools are now available. This article describes a short study that selected five suitable tools and compared their performance on nine European arable farms, concentrating on the crop production components, to determine how useful they are for assisting in the development of site-specific mitigation strategies and how well they would perform within farm assurance or benchmarking schemes. The results were mixed, with some tools better designed for identifying mitigation opportunities than others. The results also showed that, quantitatively, the results are highly variable between tools and depended on the selected functional unit, this being highly important if the wider aspects of sustainability such as food security are to be considered. However, there is statistical consistency across the tools regarding the ranking order of the farms in terms of their emissions.