I have a tape measure in mm and have absolutely no issue using it to measure things up to 5m in length. It’s trivial to convert in your head between mm, cm, and

I have a tape measure in mm and have absolutely no issue using it to measure things up to 5m in length. It’s trivial to convert in your head between mm, cm, and meters and record whatever unit makes the most sense. Or it’s also fine to just work in mm for largish objects - anyone with any experience with metric units should have no trouble visualizing a car, for example, that is 4,555 mm long. And car dimensions are routinely given in mm by manufacturers on websites, pamphlets, etc for use by the general public. So I think mm should be just fine for a bookshelf, unless it’s 10+ meters long. BTW I am an American who grew up using feet/inches, and am now a total metric system convert. I too grow tired of the endless snarky remarks every time someone uses a non-SI unit on the internet, but let’s not delude ourselves into thinking the US way (and other countries who still use non-SI units for certain applications, the US isn’t the only one although it is perhaps the worst offender) of doing things is somehow better. It’s just the convention that people are familiar with in the US.