A quantitative, analytic model of evaporative cooling covering both the small- ( 4) {eta} regimes is presented. {eta} is the dimensionless parameter defined as the trap depth divided by the temperature of the trapped sample. Although some of the same general properties present at large {eta} are also present at small {eta}, there are significant quantitative differences. These differences must be taken into account in order to accurately extract from the trapping data quantitative measurements of, for example, collisional atomic cross sections.