Eurorack modules are sized in HP (1HP = 5.08mm) width, and module depth must fit the case's clearance

Eurorack width is measured in HP (horizontal pitch), where 1HP equals 5.08mm; a case’s width in HP determines how many modules fit side by side. The second, easily forgotten dimension is depth: a module protrudes behind the panel, and shallow cases (skiffs) may not physically accommodate a deep module, so depth must be checked against the case’s internal clearance. 1U rows (a shorter format than the standard 3U) can hold utility modules like mults or audio I/O to save 3U space, but 1U formats are not interchangeable between makers (e.g. Intellijel vs Pulp Logic).

Examples

A 84HP row is 84 × 5.08mm ≈ 427mm wide. A 25mm-deep module will not seat in a skiff rated for 20mm clearance even though it fits the HP width.

Assessment

Convert a 42HP module row to millimetres. Explain why a module can fit a case’s width but still not fit the case, and what spec you must check to avoid it.