Which bar to use?

If you train at your typical Big Box Gym (24 Hour, Bally's, Planet Fitness, etc), you're not going to have this problem. If you can't lift the 45 lb standard "men's" bar, you're relegated to the machines.

But any real strength and conditioning facility or any CrossFit gym will have a variety of bars to choose from, the most often used are the 15 kg "women's" bar and the 20 kg "men's" bar. What I often see is that women automatically go for the "women's" bar, and the guys for the "men's" bar, even if that bar isn't the best choice for the movement or weight they are going to use it for. So, here are some general guidelines. 

1) Will you need to drop the bar?

If so, follow this rule of thumb: only drop a bar once the total weight in bumper plates is equal to or greater than the weight of the bar. So, if you're a guy and you only want to jerk or snatch 65 lbs, and you use a 45 lbs bar with 10 lbs plates on each side, don't drop the bar. If you must drop the bar, use a "kid's" (25 lbs) bar with two 10 lbs plates on each side. That's 40 lbs of bumper and 25 lbs of bar, totally safe to drop. 

(uh-oh, looks like you'll have to go to YouTube to watch it.)

2) Pressing vs. Pulling

One of the main reasons that a 15kg bar is nice for women is that the bar itself has a smaller diameter so it's easier for our dainty lady hands to grab. (I'm sure none of us have dainty hands anymore, though. Holla if you love your callouses!) If you're squatting or pressing, your hold on the bar isn't as essential as when you're doing deadlifts, cleans, or snatches. If you're strong enough to work in with the guys, don't shy away from using a 45 lbs bar for pressing and squatting, the math is easier and it's not going to matter nearly as much. 

I also think women should work in with the men more often. Make them nervous. 

3) Consider your warm up

If your top pressing weight is 45 lbs, you don't want to start with the 20 kg bar, and you shouldn't start with the 15 kg either. Start with that training bar your gym hopefully has at 10 or 15 lbs and give your muscles and CNS the right warm up volume to have a good shot a a PR and start making some gains!

Also, it's totally okay to switch bars in the middle of a workout. When my shoulders are unhappy, I'll start with a kid's bar to warm up movement before moving to the 15 kg bar. Ain't no shame in it.

Any other consideration I may have missed?