Miscalculate

He didn't miscalculate.

They miscalculated by assuming the dimensions were in imperial, not metric.

Hitler and the Japanese generals miscalculated badly, 10 years ago, when they thought we would not be able to use our economic power effectively for the defeat of aggression. Let would-be aggressors make no such mistake today.

Obsessed only with cost, 'Sir Humphrey' saw that Transport for London 'got away' with ticket office closures on the Tube with only minor public pushback and miscalculated that it could do the same on the national network. This assumption backfired spectacularly.