Each of the many materials budget allocation formulas developed and implemented by academic libraries is unique in terms of the variables which are included as well as the relative weighting applied to each variable. This study quantitatively compares how the differences in the composition of seven such formulas affect allocations of monograph and serials budgets by applying the formulas to a single test case, a small undergraduate library. Comparisons are made of the major discipline groups (Humanities, Social Sciences, and Science and Technology) as well as at the departmental level (sciences). Despite considerable differences in the construction of these formulas, fairly consistent outcomes are predicted. Coefficients of variation for the means of the seven formula allocations for major discipline groups range from 5.0% to 10.8%. Formulas that include a “library usage” variable do not yield allocations significantly different from those that exclude this variable. The means of formula allocations calculated for four science subjects agree with allocations derived from recent survey data for library spending in these areas to within one standard deviation. It is concluded that there is a considerable degree of similarity in the way allocation formulas function in practice.