Calculating bottom bracket spindle width

[Jeffta]

Hello,
I’ve got an old set of square taper FSA tempo cranks (2x) that I want to swap from a single speed 120 OLD bike to a 1x10 135mm OLD one.
Any tips on how to calculate the spindle width for correct chain line?
I can’t find anything for that model on the manufacturers website, and i don’t think measuring the one on the single speed will work with the different chain line.

[ReapThaWhirlwind]

Park Tool has a number of videos on how to factor chainline.

To measure from the crank, you go from the center of the seat tube to the center of the chainrings.

Typically, you have 3ish mm to work with.

Some magic numbers to remember is that triple cranks usually need 126mm // doubles use 118mm.

120mm ones are the middle ground; I think that might be like when you have a triple but can remove the granny ring.

I looked up your crank and it recommends 44mm chainline and 118mm bottom bracket—which sounds about right (same as Shimano compact road).

Make sure you match the size of your bottom bracket shell of your bike frame (68mm or 73mm).