HP (horizontal pitch) is the unit for measuring a module’s panel width in Eurorack. One HP equals 0.2 inches (5.08 mm). A standard 3U Eurorack panel is 128.5 mm tall, so width is the only dimension that varies, and it is counted in HP.
HP is also how you budget case space: a case’s rows are rated in HP (for example 84 HP), and the HP of your modules has to add up to that or less.
