This BMW tool (or a cheaper equivalent) may be useful if you want to see how much thickness each pad still has:
https://www.tillmantools.com/Baum-To.../bmt341260.htm
https://www.ecstuning.com/b-genuine-...e/83300492467/.
I'm not sure if you can measure the pads on the inside of the calipers with this tool. If not, I'd try measuring each outside pad and then eyeball its inside counterpart to estimate its thickness.
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