This study explores the doctrine of ‘agronomic accounting’ which spread in France during the first half of the nineteenth century. This in-kind accounting aimed at representing, in the most complete way possible, the techno-economic flows that take place within farms, so as to optimise their productive efficiency. As such, agronomic accounting epitomises a broader notion of ‘yield’, as part of an energetic understanding of production that was gaining traction in various industries at the time. We present the genesis of agronomic accounting, before dealing with the issue of the choice of accounting units – with a specific focus on the combination of in-kind and monetary accounts – and finally showing the artificiality of the notion of yield. The research calls into question the notion of ‘agricultural yield’, metrologically ill-defined, but which nevertheless remains at the heart of all socio-economic debates about agriculture. This history of a crucial moment in agronomic metrology allows us to better understand the stakes behind a still acute issue: knowing how to feed humankind, in the most efficient way possible.