Standing is usually worth one gear shift, i.e. if you're sitting and you need to shift down a gear you can stand and keep going. Likewise if you're standing and the gradient eases a bit you can sit instead of shifting up.

I've seen thoughts that if you're lighter than you should stand 2/3 and sit 1/3, for longer climbs. If you're better sitting then 1/3 standing, 2/3 sitting.

If the hill is short, like up to 400-500 meters, then it's almost always quicker to stand. You'll be more tired though. You can explore limits, using gears that you aren't thinking of right now. This story shows how I learned that you can turn big gears on steep hills (the hill in the story is about 14-16% grade; recommended gear was a 53x15). When I'm in doubt I'll hit a hill in some stupid big gear, literally like a 53x12 or so, and just see how far I can get. It's a real eye opener sometimes.

If the hoods seem high when you're standing on semi-steep bits (like up to 18-20%) then you may be able to lower your bars a bit. The steepest I've done is about 20-22% and I had to do it sitting because the rear tire slipped too easily. 15% and the hoods are ideal.