yeah, I was wondering how long a brake line should be for a 24" kh muni.
I measured and came up with 20"
does that sound right?
also, I have a really low seat on it.
If you don’t want to have to do any mods to it, you could just wrap the excess around the frame tube.
You have a low seat now but you will probably grow a lot soon so dont cut it to just fit the low seat or you will need a new brake line later.
Well yeah but if he gets a rear brake then the cable will be very long. I used to use an uncut rear brake on my muni and I had to wrap it around like 20 times so there was a huge ball of rolled up cable. Kris Holm laughed at it.
hahaha!
I cant say how long to cut it, but keep some growing room in there.
The main thing is to have some excess length to allow you to put your seat up, should you ever need to in the future. Also if you ever get shorter cranks you’ll need a higher seat and hence a longer brake line. Wrapping excessively long brake lines around the frame looks hideous IMO.
If you ever have to dismantle your uni I suggest you keep the line long enough to be able to get the seatpost out the frame, else you either have to remove the handle from the saddle or the slave pistons from their mounts. I use a stock front brake that goes once round the frame. Are you cutting it down yourself or getting it done professionally? With the magura kit altering brakes is pretty easier, and for me it was cheaper to get enough stuff to do it several times than to pay someone to do it once, and I could be assured the length would be correct.
The braided steel line on the custom set sold by UDC is 17.5" long.
really? that seems pretty short…
Yep. It’s laying straight out on the workbench, so it’s an exact measurement.
Fits my KH24 with 137 to 165 cranks no problem. I’m 6’ tall.
wraping it to many times will decrease braking performance and break lines earlier.
jus cut it and if you need a new one a steal braded goodridge isnt that expensive.
ok cool.
I think I’ll do 16.5" then
does this sound good?
If you are using the KH seat post adapter, it should work fine. You can always use a stiff wire like a coat hanger to get an actual length; just mount the lever and the brakes, and bend the coat hanger to fit. Measure twice, and cut once. 
Pics when you are done.