Metering With Flash?

I used to wonder why my exposure meter would tell me there wasn't enough light, but when I take a picture with flash the pic comes out fine. I'm guessing that the metering doesn't account for Flash. Am I right?

Correct. Metering meters ambient.

how do people meter with flash then? Does it have to do with TTL?

The problem is that the flash is too quick. Even if the meter measures the flash, the display would go back to measuring ambient light when it was over. You can get a hand held flash meter for metering flash. They will measure the flash, and keep the settings displayed.

My Canon DSLRs have a Flash Exposure Lock (FE Lock) feature. I've never used it, but I think it's pretty much a flash meter of sorts. Check out your camera manual.

You can also figure out flash exposure using this formula: Guide Number divided by distance to subject = f/stop. You can find the guide number in your flash manual or at the manufacturer's website. It will usually be listed in feet and meters and for ISO 100.

Example: If my flash GN is 110 (feet) @ ISO100 and my subject is 10' away, then at full power "correct" exposure is f/11 @ ISO 100. If I wanted to use a larger aperture (smaller f/#) I could reduce the ISO or flash power or increase the distance between flash and subject.

Every halving or doubling of the flash power or ISO is one stop.

Every halving or doubling of the distance is 2 stops (the inverse square law). In the example above if the subject was 20' from the subject the f/stop would be f/5.5 which we'd round to f/5.6. F/5.6 is two stops more light/exposure than f/11.

Personal testing is a good idea. Sometimes it can seem like the flash manufacturers exaggerate the GN a bit. With some of the cheaper flashes I've used I've found I need to add a 1/2 stop or so to get what I consider "correct" exposure.