The exchangeable acidity determined by neutral 1N NH4OAc was compared to that measured in a buffered solution on 348 soil samples from profiles of Red‐Yellow Podzolic soils in Alabama. The soil pH values ranged from 4.1 to 6.5 and cation‐exchange capacities from 0.8 to 13.0 me. per 100 g. The methods measured comparable amounts of acidity. An equation was calculated by the method of least squares for the relationship between soil pH and percent base unsaturation for all samples. The amount of CaCO3 needed to bring soil pH to desired level was calculated by estimating percent base unsaturation from soil pH values in water and by measuring exchangeable acidity of soil by pH values in a buffered solution. The validity of this procedure was tested by incubating soils with increments of Ca(OH)2 and measuring the change in soil pH.