We developed a technique to measure the projected leaf area of plants any time during the day or night. “Projected leaf area” is the leaf area seen from directly above, and is the area most likely to intercept herbicide spray from an over-the-top application. The technique involves photographing a plant and a reference square of known area from directly overhead using a light-tight box containing a flash unit. Negative images thus obtained are reflected (by means of a slide projector and mirror) onto filter paper lying on a glass stage. The projected leaf area is determined by planimetry of the negative image of the leaves and the reference square. The projected leaf area can be compared to the actual total leaf area after one determines the latter with a conventional area meter.