This protocol provides step-by-step instructions for estimating cover crop biomass using ground cover photos and height measurements. Compared to traditional destructive sampling techniques, this method is an inexpensive and efficient option for monitoring cover crop biomass with relatively high accuracy. Because the field assessment requires minimal technical expertise and equipment, it is also particularly well suited for citizen science and other applied research contexts aimed at generating large, geographically distributed datasets. For instance, in a two-year study of cover crop performance in the Great Lakes region, the field assessment allowed for collecting cover crop growth data from 257 fields across six states. To validate the accuracy of the field assessment and derive relationships for converting the field assessment output into standard biomass units (e.g., kg ha-1), cover crop biomass was also destructively sampled with a quadrat from 111 of those fields. The R2 values for relationships between the field assessment output and biomass validation samples were 0.84 for cereal rye (N = 55), 0.76 for single-species cover crops more broadly (N = 73), and 0.79 for multi-species mixtures (N = 38). Linear equations were then derived for each of those cover crop subgroups to calculate biomass in kg ha-1. We recommend following a similar validation process when using the field assessment in new regions or contexts. The protocol below is divided into three sections: 1) estimating single-species cover crop biomass; 2) estimating multi-species cover crop biomass; and 3) validation procedures.