Coseismic landslides have been one of the major causes of human suffering and house damage in recent large‐scale earthquakes. Estimating the occurrence of coseismic landslides in advance is important to promote rapid and efficient emergency response and disaster prevention measures in advance. Various previous studies have been conducted on landslide hazard assessment. Methods that can evaluate the occurrence site over a wide area can “relatively” evaluate the hazard and probability of occurrence, but cannot “absolutely” quantitatively evaluate the area of collapse or the amount of collapsed sediment. In addition, methods that can quantitatively evaluate the scale of collapse cannot evaluate the location of landslide occurrence over a wide area. Therefore, based on the actual results of landslides during the 2016 Kumamoto earthquake, we developed a formula for estimating the logarithmic landslide cell percentage (log(P)) for a range of topographic and geological conditions. The log(P) obtained from the estimation formula for each range is consistent with the actual results of the Kumamoto earthquake regarding the following three points: total landslide area, trend for increase of actual landslide cell percentage with increase of log(P), and correspondence of actual landslide cell percentage and estimated landslide cell percentage with the cells belonging to the log(P) class. From these results, we judged that the developed estimation formula can represent the actual results of the Kumamoto earthquake in terms of the spatial and quantitative absolute index. Then, using the 2008 Iwate‐Miyagi Nairiku Earthquake as a verification example, the estimation formula was applied to an area with similar geological features. As a result, it was found to be well suited to the validation data with similar topography and geology. And the effectiveness as a quantitative absolute index was shown even in different regions.