This paper reports estimates of TV white space (TVWS) availability in Japan that are based on the separation distances calculated using D/U-based and I/N-based rules. Calculating the TVWS availability with various TVWS-device parameters—antenna height, transmission power, protected area threshold, and adjacent channel leakage ratio (ACLR)—revealed the parameter dependence of the availability of TVWS channels. The effect of changing the protected area threshold is shown to differ between D/U-based and I/N-based rules: only in D/U-based rule do both separation distance and protected area decrease when the protected area threshold increases. We also show that the effect of the ACLR is smaller than that of the other parameters. Our estimates can be utilized as reference data showing how changes in TVWS availability depend on various TVWS device parameters.