There are two kinds of microsprings often used: box microsprings and zig-zag (serpentine) microsprings. Box microsprings are considered with larger spring constant k and more symmetric structure keeping balance than zig-zag microspring. Density of spring number, N, is defined as the numbers of turns within a constant total spring length to investigate performance of box microspring. With applying the same force, the relation between spring constants and microspring sizes are discussed. Under different size parameters of box microsprings: B, W, T, and L, the spring constants decrease like exponential decay and approach a limit value as density of spring number increasing. The results show density of spring number has significant effect on spring constant. Rate of change on spring constant, Kt, is defined as the ratio of spring constant between N=1 and N=10. It means normalization of spring constant that increase density of spring number from minimum to maximum. The results show Kt decreases when B and W increase and increase as T and L increasing. Therefore, the spring constant is coupled affected by different size parameters due to different tendency as results shown. Such that the results can apply in microspring design by adjusting these size parameters to obtain the spring constant.