The sieve test is a method of measuring grain diameter for erosion control studies using a sieve made from a wire mesh. However, it is expensive to transport gravel from the field to the laboratory. Therefore, we looked for an easy, economical method of measuring grain diameter. We proposed a simple method for measuring the grain diameter in the field. Our method uses the contact time between the gravel and an elastic body. We determined the contact time between glass balls, gravel, and a hard plastic polyacetal board and found that the grain diameter was proportional to the contact time. Experimentally, there was a good correlation between the contact time and grain diameter. In addition, the count of the number of pieces of gravel was accurate. The contact time was measured and converted to the grain diameter. The resulting grain size histogram of the gravel determined in the experiments matched the material studied. Application of this method in the field is possible.
