A number of factors are considered to determine the appropriate ratio, such as the ecological type of the wetland and the proposed mitigation, whether the wetland being impacted is rare or imperiled, and the method of mitigation employed. Mitigation ratios can require as little as 1.5 acres of mitigation per acre of impact (1.5:1), to over 5 acres of mitigation per acre of impact (5:1). If a permit to use or develop wetlands is acquired after-the-fact, the ratio will be doubled.