Agricultural Land fragmentation is a global problem in various magnitudes, but the disaggregated effect of field shape, size, and distance has not yet been established. Simple measures have been applied to estimate the aggregated effect of land fragmentation on farm performance. This paper contributes by introducing a new joint index for field shape and field size, field viability index (FVI), aiming at measuring the effect of land fragmentation on farm performance based on field characteristics. The index is calculated for Danish wheat fields and is tested on a large sample of Danish farmers showing a significant effect on yields. Further research may involve estimating the effect of field characteristics on the aggregated economic farm performance. The field viability index has multiple applications in e.g. benchmarking, leasing or buying arrangements, and for identifying potential land consolidation projects.