duh who wrote:

One is facing width. I'm doing a coat. What's an adequate setting? 1.5
inches? 2 inches.

Are you lining it? (Check some high-quality RTW garments in as close to
the same style and see what they do)

Is this your mandarin-style coat? (You can put a binding around the
edge and bind in the outside fabric and the facing if so)

The other is hem allowance. What would that be, about 1 inch? 1.5 inches?

When I took sewing lessons back in the dark ages, they said that the
ideal hem was something like 2-5/8 inches. But I have since read that
(a) the more flared the garment, the narrower the hem should be while at
the same time reading that (b) the wider the hem in general, the better
quality the garment is considered to be. But see above if this is that
mandarin thing, because a self-binding around all the edges would look
really nice and you would need neither facing width nor hem allowance.

Yes, you will get to the point where you can figure all this out on your
own. Ask lots of questions, look at lots of patterns (even ladies' wear
if it's the same style) in the fabric store or online to see
construction details, and you will get there faster than you can imagine
possible.

If you have a plain straight coat, 2-5/8 inches sounds reasonble to me,
or make it an even [sic] 3 inches.

--
I know God will not give me anything I can't handle.
I just wish that He didn't trust me so much. - Mother Teresa