Metric or Imperial - which do you use?

How do you measure distance? Do you convert road signs into km?

Good question. My sat nav thing on my phone is set to km, when I talk to people about distances I'll most often say how many metres or kilometres away something is, if I'm exercising indoors or outdoors (e.g. on a treadmill or out running) I'll use kilometres and kph, I'd measure things in millimetres or centimetres. Obviously if I was to drive I would have to pay attention to miles per hour, but with a sat nav I wouldn't need to think about how many miles my destination is away from me, as it'd all be in kilometres anyway.

So in reality you use both then.

When I start driving (not yet) I will be forced to use both. That isn't the case right now, but even if it was, the vast vast majority of the time I'd be using metric.

And the waist size on your trousers? In inches?

Well, considering there are substantially more units derived from metric rather than imperial...

https://en.wikipedia.org/wiki/SI_derived_unit

If you really want to, you can derive them all in imperial.
1 Hz = 1 s^-1
1 rad = 1 rad
1 sr = 1 sr
1 N = 1 lb * const
...

Besides, I'm pretty sure you could have imperial units for the thing you're measuring, provided conventional use with equations. For example, energy is foot-pound(force), momentum is pound-feet/second, and so on. There could even be imperial electrical measures if they adopt Amps and Coulombs like they did with seconds and radians (eg Volts = foot-poundf/coulomb).