Eurorack Dimension Questions and Help

As the title implies - this thread is for Panel Dimensions, Rail Sizes, DIY Case Information, etc.

I will start off with a Diagram that seems to have helped MANY beginning DIY’ers.

This is from Doepfer’s website that contains all of the details of the A-100 Case Construction.

This diagram however, confuses me.

Here is why, and maybe, hopefully, someone can shed some light on this aspect.

1hp = 5.08mm
2hp = 10.16mm
and so on.

hp is multiples of 5.08mm

and here is my confusion -
1hp Actual Module Width = 5.00mm
2hp Actual Module Width = 9.80mm
and so on…

^ what in the actual #$%@ (lol)


Nothing constructive to add but that’s the reason why I went Kosmo format.
Bought the cheapest eurorack pair of rails that use sliding nuts I could find and I’m using those as default size of my case.

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If I understand your confusion correctly, the answer is on the page:

The actual width of a front panel is a few tenth of a mm less than the calculated value (i.e. multiple of 5.08 mm resp. multiple of 1/5") to have a little bit tolerance to assemble the panels.

Though it does seem like a 2hp module should be 10mm.

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The ones that really get me are when you get into the larger sizes and the differences are vast… like
14hp = 71.12
14hp Actual Module Width = 70.80

^ thats like… not a small difference… lol

The reason this is bugging me is because I am trying to make a custom case but I have no clue how wide to make the rails so that when modules are in it, there isnt a shit ton of gaps… lol

But going by that guide is confusing as hell.

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Yeah, this one cropped up for me too a while back. In the end I went with ‘Buy rails and end cheeks, assemble and measure’, which is a valid option if your buying premade rails. However if you want to make your rails too, Synthracks have a handy dandy guide to how long they should actually be (based on the ones they sell) so you can build custom cases -

It also lists common panel widths and the actual height they are expected to be (cos they are slightly smaller than 3U to boot). Again, these are not actually a ‘standard’ but they have matched up with all my purchased modules dimensions so I am guessing they are correct.

[EDIT] Just realised the original Doepfer article also lists the correct panel height. I must have been hasty back in the day and missed it… doh!

I think it basically comes down to how companies want to round their measurements as the Rack Unit is measured in Imperial and everything else about Eurorack is measured in Metric.


I’d say 0.3 mm is pretty small :slight_smile: (12 mils, 1/80th of an inch, four human hairs…)

Looks like they’ve chopped off about that much on most panels, “to have a little bit tolerance to assemble the panels.” The module width is the grid size, after all. You want to make the panels a tiny bit smaller so they fit.


Basically it’s “1HP = 0.2 inches = 5.08 mm but shave a bit off that to make sure things fit” and Doepfer tells you how much they shave off, but other makers might shave off a little more or less. A few tenths of a mm one way or another isn’t likely to cause trouble. If you really want to make sure your modules fit tightly with no gaps and no overlaps, use slide nuts, but I use threaded inserts and don’t worry about the tiny tiny gaps.

The thing that really causes trouble is a few makers use a different system for the distance between the edges and the mounting holes. Not sure who but I know GMSN was one. The difference is several mm, even at the extremes of slotted mounting holes. I ended up enlarging the slot to get my GMSN module to play nice with the rest.


THE WORLD NEEDS TO BE SEAMLESS GOD DAMMIT… :stuck_out_tongue: :stuck_out_tongue: :stuck_out_tongue: lol.

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But no seriously, thank you everyone for the help.

I am friggin AWFUL with measurements… didnt have a ruler or a caliper on hand lolol. was just reading numbers on a laptop screen without thinking of any conversions haha.


If you want to make your own panels with your own hands, you definitely need a good ruler and caliper. This photo says all :stuck_out_tongue_winking_eye:


As it’s all on sliding nuts, you only have one gap and that’s at one end or the other of the run.


Check these out :smiley:
A 4hp 3u hp Ruler -

and a 60hp 1u hp Ruler -



Hey man, I get the confusion. Had the same worries,

I finally settled on lasercutting a wooden rail that has 3mm holes spaced 5.08mm apart, and that should work out fine I hope, but I won’t have any “official” modules to test it.

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