Ha. Maybe a VERY short climb. That's about 10 watts/kg

I'm old now but I used to do repeats on Chesterfield hill-9% grade and .75 mile. I could only attack standing for about a quarter mile even at the peak of fitness. The next quarter mile I would spin in mid range gears and then stand again for about and eighth of a mile and then spin to about fifty yards from the top and then balls-to-the wall standing to the top. When I was 50 I was often among the first riders to crest the hills in the A-group on club rides. I was awesome. I still am actually but to humble to brag.

I do that on one of my local hills. It's a 4-5 minute hill for me and I'll alternate standing all the way, sitting all the way, spinning the smallest gear I have, mashing the biggest gear I can handle, just generally mixing it up.

18-20% is "semi-steep" is it? Only on the 41....

I was cycling up those hills mostly in sitting position. On longer hills it gets pretty monotonic, mentally tiring and would get me all stiff. So bit by bit I would start to climb out of saddle. In the beginning I'd grossly misjudge my efforts and blow up pretty soon. Then I would have to sit and my overall speed would drop big time. But over the time I've learned how to pace and now it does not matter much. I can go either sitting or out of saddle for an hour. The average power in case of out of saddle is just a bit higher with the same perceived efforts (my out of saddle cadence is very low). What I did noticed though going out of saddle has greatly increased my hiking abilities. I cycle whole year but I only hike very short time in the summer. So when the summer starts and I go hiking I would be completely out of shape. No longer the case.

I actually did experiments climbing steep slopes seated and standing with the power meter, and, at least in my case, standing resulted in a noticeable hit to my sustainable power. To the degree where I could put out 250-280 W for the duration while sitting, but only 180-200 for the same period of time standing. To make matters worse, I can go 280 W sitting for 8 min and I'll be recovered fully within 10 or 20 minutes; but going 200 W standing for 8 min causes physical muscle pain that does not go away for the duration of the ride.

I have no doubt that this can be trained for, but, for an average Joe, climbing out of the saddle is a last-resort option whenever you're out of gears.

Funny, I tend to work on my seated climbing lately as standing feels easier to me. I can push higher watts standing and feel less fatigued. I am talking about 1 hour plus steady climbs at ~5%. I come from a trail running background.

On my commute home I have a nasty pair of hills to finish the ride (we live at the highest point in town). My goal is to stay in the big ring all the way up and over - in fact, yesterday was my first big-ring ride home of the year. I like to get to the point that I can do the entire hill out of the saddle - once I get there, I like to work then on spinning up.
On "road rides" I like to pop out of the saddle on hills to work the legs and lungs differently, it feels very refreshing sometimes to stand and put everything into a different position.

Running is competing for time in the saddle as my primary workout activity. Climbing out of the saddle, 2 or 3 gears up, is very pleasurable and seems to engage bigger muscle groups. Yet, on long rides I think it's shows itself as big time gas guzzler; spinning is a 4 banger, standing is a V8.

In Switzerland a family friend lives up a road so steep that as a kid I thought the car was going to tip over backwards going up the thing. It's considerably steeper than the 16-19% grades I've ridden/driven up. With all of the 25% pitch roads in the various Grand Tours I figured 18-20% is "steep but not excessively so". You can big ring it for a bit.

So 18%-20% is semi-steep but the steepest you've done is 2% more? Something isn't right. Perhaps your 41 logic

Keep in mind that wind etc play a part at pro speeds. They'll slow for switchbacks, speed up for the straights, and if they're sheltered from the wind they can get going pretty well.

There's a story about a (new to covering cycling) journalist that was on a moto in a race on some climb (this was in VeloNews or Bicycling or something like that). The much-more-experienced driver was trying to be "user friendly" and was commenting on various things, speed, grade, etc. The driver said, "They're going 25 so that's a decent pace". The journalist, a US person, did the conversion. 25 kph is 6+6+3mph so about 15 mph. Okay, that seemed reasonable, but a bit slow. The journalist asked, "wait, they're going 15 mph?" "No, no, no," the driver replied, "They're going 25 mph. I converted from kph for you."

Pros are soooooo fast.

I went to watch the Philly race a bunch of times. One year Sean Yates won, solo. I was on the finish loops and didn't see him at all. I only saw the motorcade blasting by but not him. I didn't realize until after the race that the motorcade was just behind Yates - they were going so fast, in the 35 mph range, that I didn't think a rider could stay with them even temporarily, forget about 150 miles into the race (the neutral start is usually in the 30-32 mph range, so fast that when a domestic pro flatted he couldn't get back on, the team sent two guys back, and it took them forever to get back on the field). When Yates won I'd been racing 13 years, I had watched the (then amateur-only) National Crit Championships, I'd raced in Belgium (for only 3 weeks) where in my first race I got shelled in 5 km when my max speed was 43 mph / 70 kph (on a flat course with cobbles)... I thought I understood what "fast" was but I didn't. The speeds pros hit and maintain are incomprehensible.

At a local race (that I promote) one domestic pro team sent one of their stronger riders, sort of for entertainment value. It's sort of like if, say, Cancellara showed up at a local club's TT (but this guy was no Cancellara). On the first lap he went to the front and started pulling. Only 5 guys could hang on his wheel after one lap. 1 guy was left after two laps, and that guy got 3rd at the Elite (aka pro/am) National RR Championships a few years prior, so that guy was an absolute top level Cat 1. On the third lap the Cat 1 was gone. In about 8? 10? laps the pro lapped the field. He hung out at the back of the field and chatted for the rest of the race. He made the local Cat 1s and 2s look like Cat 5s doing the first race of their lives. Really incredible.

So he's strong, right? Well this domestic pro team went to Tour of Georgia. I expected to read at least about that guy, like maybe he'd place top 5 or something, some unexpected domestic team's surprise rider. Nope. The only way he could get any publicity was to attack at the start of a long flatter stage. He was away for something like 80 or 90 miles but faded hard long before the finish. The team was absolutely destroyed in the race. I ended up looking for their riders from the bottom of the results page, not the top.

A friend of mine raced in Europe for 7 or so years, pro. Never made it to the big teams but raced for the feeder teams. He'd come back for vacations, visit his family, etc. He came to my race. He attacked early on, got away solo. Because he's a local, because everyone knew him, because everyone knew he was a pro, everyone chased, and I mean everyone. The field was single file the whole race, going flat out. He never got a big gap, max 20 seconds or so, most of the time literally just 10-15 seconds. Yet he persisted staying out on his own. Me, personally, I'd have sat up if I was soloing for, say 20 miles without getting more than couple hundred yard lead. He got caught with about 600 meters to go, where I happened to be marshaling. I went back to the finish to do race promoter stuff and saw my friend. "I'm sorry you didn't win, I can't believe they caught you with half a lap to go" "What do you mean?! I won the race!" "You won?!" "Yeah, when they caught me I just stayed on the gas, led out, and dropped them in the sprint!"

A later year a Kenda/5-hour pro did the same series of races. He could win solo (lapped the field, but not quite so decisively as that one guy). He won a few races - it was so hard to beat him. I asked him one day if he gets tired of winning. He laughed. He said that in a pro race he's everyone else's b*tch. He says after he wins a race or two here he won't win for the rest of the year. (Disclaimer - it ends up that he had some kind of cancer at the time, didn't tell anyone including his team, but he's recovered and has won a couple races here and there, but not many people would know who he is.)

Someone posted something maybe 5-7 years back comparing wattages among amateurs and pros. They realized that the magnitude of difference between a Cat 5 and Cat 1 is LESS than the difference between a Cat 1 and a higher level pro. In other words if you become a Cat 1 you're closer to a Cat 5 than to a Euro type pro.

No, I don't think I've ever done a 20% hill. 19%, yes for sure.

"Steep" is stuff that I haven't even tried. I was just toning down the magnitude in an effort to defuse the guys who'll pipe up and say "yo moron, 18% isn't steep unless you're a wimp, 25% is steep!". To me 16% is steep, else I wouldn't have pestered my friend on what gear to use on such a hill (remember he said a 53x15 - that's not a gear you use up a steep hill, in most cases, and this conversation took place when we were 14 and 15 years old). 19%, there's a short little hill near Nytro and someone next to me said his Garmin said it was 19% - for me it's short enough that I'd rather 53x15 the thing than 39x25 it.

I've declined rides where they planned to hit hills over 20%, like 22% etc. I don't see the point in climbing such hills. Those are "really steep" hills to me, the ones I prefer not to do.

I know there must be calculated tables for that somewhere. Got a link? I could start reporting some of the suspect Stravas around here...

Agree. And you tend to see that skill in smaller/lighter riders for some reason.

No link, calculated it.

Air density = 1.15 kPa
Rider weight = 155 lbs (70 kg)
Bike weight 15 lbs
Crr = 0.0033
CdA = 0.35

Hill power = mgv*sin(arctan(grade/100)) = 77*9.8*9.8*0.06 = 444 watts
Wind power = 0.5*rho*Cd*A*(v_relative)^2*v = 0.5*1.15*0.35*9.8^3 = 189 watts
Rolling watts = Crr*mgv = 0.0033*77*9.8*9.8 = 24 watts
Add ~5% for bike efficiency = 0.05(444+189+24) = 33 watts

Total = 690 → 690/70 = 9.9 w/kg

This is a great vid on climbing. Kind of point to positives of both seated and standing

https://www.youtube.com/watch?v=zam74qlzGtQ

you can also turn it around and use a slower cadence and slower speed while standing to rest a bit. I'm smaller and if i had my choice i'd be standing on every hill but there is a length limit for that.

In addition to what others have said, standing can help flush out lactic acid that may have built up in your legs. Also, it's worth noting that a pro can shift into a higher gear for a standing climb than the vast majority of recreational cyclists. So it can definitely work for them, but the odds of it working for a typical cyclist are much different.