A Reasonable Approximation

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How tall is the Shard, really?

According to Wikipedia, the Shard (the tallest building in the UK) stands "309.6 meters (1,016 feet) high". I put this in my Anki deck as "Height of the Shard / 310m", but I was saying "height" to mean "tallness" (because I don't much like that word) and I had assumed Wikipedia was using it the same way. So I thought the Shard was 310 m tall.

But according to Bron Maher in Londonist,

most sources put the building’s tallness - that is, its length base-to-tip - at about 306 metres. The last three metres come from the height of the ground on which the Shard is built. So while its height is indeed 309 metres above sea level, the Shard is only 306 metres tall.

Is that so? I was curious enough to investigate1, but it turns out I don't really know how to.

(Also: Maher says the Shard is 306 m, not 309 m, not "not 310 m". And he gets 309 from Wikipedia, quoting it on the list of highest points in London, which talks about "the 309 m (1,014 ft) tall Shard". Where did those extra 60 cm go? The article on the Shard itself also has that number, in the "records" section near the bottom, but the infobox on the right has 309.6/1,016. So is it 306 m, 309 m, or 309.6 m?)

The boring investigation

The first thing to do2 is to look at Wikipedia's sources. It doesn't have one on the list of highest points, and it doesn't have one in the "records" section. The infobox does have a source for the height, which is on skyscraperpage.com. It lists the spire at 1,016 ft or 309.7 m, yet another number! There are various drawings, all giving the roof at 304.2 m and the spire at 309.7 m. (1,016 ft is 309.68 m, but 309.6 m is 1015.75 ft and 309.7 m is 1,016.08 ft. So if you convert 309.6 m to feet and back to meters, you could get 309.7 m. But wikipedia shouldn't be taking 309.6 m from that page.)

Skyscraperpage lists the source for the height as http://www.the-shard.com, and the about page on that site says: "How tall is The Shard? The Shard is 309.6 metres, or 1,016 feet, high and is Western Europe's tallest building." You'd certainly expect the Shard's official webpage to be right about this, but also it says "high" not "tall" so it could be a misdirect.

Next3, does Maher have any sources? For 306 m tallness he just says "most sources" give that figure. For 3 m above sea level, I think that comes from its height at the top. He quotes someone at Ordnance Survey saying the top of the Shard is 308.9 m above sea level, which gives around 3 m for the base.

Most of my research was just googling things. Search terms included "how tall is the shard", "height above sea level of the shard", "the shard architectural drawings", "uk contour lines" and "ctbuh the shard" (inspired by one of the earlier results). Here are some of the things I found.

The London Pass: "The Shard is 306 metres tall, however if you measure all the way up to the tip, it's 310 metres". I don't know what point below the tip it's talking about. It could be roof versus spire, but the skyscraperpage drawings give a different roof height.

The Skyscraper Center: height ("measured from the level of the lowest, significant, open-air, pedestrian entrance") is "306 m / 1,004 ft", both "to tip" and "architectural". (The difference being things like flagpoles and antennae, which the Shard doesn't have. The highest occupied floor is "244.3 m / 802 ft".) Seems like the kind of site that knows what it's talking about. Doesn't cite sources, but the drawing they have is labeled a CTBUH drawing, and that also sounds like the kind of organization that knows what it's talking about, giving me a new google search term.

SkyscraperCity: says both "309m" and "310m" with no apparent shame. But also, that link points to page 833 of 1385 of a discussion thread4, and at this particular point people are discussing its height above sea level. (And comparing to the then-future "The Pinnacle", which became 22 Bishopsgate.) It seems the Shard is level with The Thames nearby, which at that point is tidal. Some commenters think that means it's at sea level at least some of the time, but someone else points out no: "A river can be tidal some distance above high water mark for the sea. Consider what happens when the tide comes in - the sea effectively "comes up" the river mouth, which will slow down flow of water down the river, which will start backing up. As it backs up, the level upstream will increase as less water is getting out. Thus a river can be tidal above the high tide point of the sea itself." Makes sense to me.

Someone else says it's 16 m above sea level according to Google Maps, but I can't find that info on Google Maps myself. (But it does label it as "306m-high glass & steel tower with views", if I'm zoomed in the right amount. I can't see that string anywhere else.)

Another says it's 16 m above sea level, according to "the Ordinance Datum figures". Presumably they mean Ordnance Datum; that's not a source, their point is to talk about "what is the zero-point that this is 16 m above".5 (In different comments they say 16 or 17 m, but I'm pretty sure they mean 16.)

On the next page, someone links to a nearby ordnance survey benchmark which seemingly puts the ground there at 4.563 m above sea level. (But we get 3dp precision for the height of the mark above sea level, and only 1dp precision for its height above ground level, which is sus. Probably best stick to 4.5 m above sea level, and then the Shard would be somewhat close to that - unless there are steps or a steep hill in between, and I'm sure there are some nearby.) (The benchmarks site doesn't have an FAQ entry for "what actually are these things we've catalogued so painstakingly", so here's Ordnance Survey explaining them. I think "cut mark" just means "we marked the location by making a cut in the wall somewhere".)

Someone else on the next page says Bing Maps has an Ordnance Survey overlay. Looking at that: the Shard is contained in a fairly small contour line, but that line isn't marked with a height. The next-nearest contour I can find is marked 10 (which is in meters), so this one could be either 5 or 15, making both 16 m and "somewhat close to 4.5 m" plausible, which is frankly ridiculous.

There's this topographic map. It doesn't have the Shard actually labeled, but clicking various points inside its outline I can get between 15 and 20 m. I don't think there's actually a 4-6 m difference between different corners of the base of the Shard, so this seems unreliable. And points near the benchmark seem to be about 12-15 m. It's plausibly using a different zero point than Ordnance Survey?

I couldn't find any more topographic data for free. This site might help, but I'd need to register for an account and I'm not sure that would be enough.

This pdf hosted on the CTBUH domain says 310 m height. There's also this pdf which doesn't give a height, but does have a ground configuration table; we have "made ground" from +4.7 m OD to 0.0 m OD, matching the OS benchmark. Other pdfs in the search result say 306 m, 306 m, and 1,016 ft / 310 m.

Wikiarquitecture: 310 m.

This drawing: 306 m.

And that's it for googling.

Oh! This is kind of embarrassing to admit, but even though I go by the Shard pretty often I don't have a good sense of the road layout near it, or indeed which building in the road layout is the Shard. (When you're next to it and not looking up, it's much like any other building.) But scrolling around street view for a bit to refresh my memory, I realize it has ground-level exits on at least two different floors, with an outside escalator that's probably something around 10 m elevation. (On screen it's about 4.5x the height of that guy, so I'd guess a bit under. And I think I count 36 escalator steps, this says typical escalator step rise is 8 1/2 in, which makes 7.77 m.) There's also a pedestrian walkway going underneath the level of the upper street, but that's too wide to think of as a bridge. So actually, a 4-6 m difference between corners is totally reasonable; what counts as "ground level" when you're inside a building like that? Still, the topographic map disagrees with OS about the benchmark too.

I searched HM Land Registry for the Shard, but the results don't give me anything interesting. It was a long shot.

And my final source is the aviation charts for nearby London City Airport. (Thanks to Tobias at Zurihac who suggested these and showed me where to find them.) They're on this site which doesn't like direct linking, so you have to go to "Part 3 - Aerodromes" -> "AD 2 Aerodromes" -> "EGLC London City" -> "EGLC AD 2.24 charts related to an aerodrome" -> "Control zone and control area chart", and that gives you this pdf. The Shard isn't named, but there's something there with height marked as "1015 (1008)" in its rough location, so let's assume it's that. This is presumably in feet, and Tobias thinks the 1008 is height above ground. This matches what is presumably the Crystal Palace transmitter south and slightly east, at "1087 (732)", or "331 (223)" in metres, which is close to Maher's figures for it. (Maher has it 222 m above the ground, but I'm not investigating that.) So in metres this is 309.4 (307.2), but since that's rounded it could be 309.2-309.5 (307.1-307.4).

The exciting conclusion

So… I'm not sure, really. I think my best guess is that it's 306 m tall according to some perfectly reasonable way to measure that, possibly the most reasonable. This is consistent with (i.e. lower than) the heights given by both OS and the aviation charts, and those are close enough that the difference might be caused by differing ideas of sea level. And it's the only number I remember seeing lower than those, other than the aviation charts.

If this is right then it's about 3 m above sea level at the ground, which is close enough to the benchmark height that I can believe it. I don't think I believe the "16 m above sea level" value; even a combination of "confused about which street level we're measuring from" and "differing ideas of sea level" seems like it couldn't give that. I also don't think I believe the 4.7 m from the ground configuration table - that table suggests that before development, the ground there was within 5 cm of sea level, and in particular below the nearby Thames most or all of the time. Not inconceivable, but in context I doubt.

This makes the aviation charts wrong about its tallness, which is my biggest sticking point here. But I'm not sure how reliable to expect them to be about that. Height seems far more relevant to their interests than tallness, and they could easily be using a ground-height measurement at some nearby point.

I think the funniest way to resolve this for good, would be for someone to announce plans for a 307 m tall building with its base 4 m above sea level, and specifically claim it as taller than the Shard. The skyscraper fandom will presumably erupt into civil war, but when the dust settles we can hope they'll have uncovered the truth.

Why is this answer so hard to find? It feels like the sort of question that has a single definite answer that you can just look up, but clearly not.

It's probably relevant that I can't easily check for myself. I suppose I could use a sextant or look at shadow lengths. But those will both work best if I'm far away, and then other buildings make it harder plus I might no longer be at ground level. I don't think I can even get to the top, let alone dangle a tape measure from it. I think GPS gives me height above sea level, but I'm not sure how precise it is, how accurate it is (especially when surrounded by buildings), and again I can't go to the top. So if two sources disagree, there's no obvious way for me (or probably most people) to check which if either is correct. But why do sources disagree in the first place?

Sometimes with tall buildings the issue is that there are multiple things that could be considered "the top". Two sources suggest that might be happening here. But they still disagree, and the Skyscraper Center suggests it's not.

Might it be that different sources define sea level differently? Perhaps, but this isn't enough by itself unless someone used different sea levels for the top and the bottom. I'm not sure how much difference we can expect this to explain.

How about forgetting the difference between height and tallness? This does seem plausible to me. I could imagine someone standing at the top of the Shard with a device telling them they're (say) 309.6 m above sea level, and forgetting to also use that device on the ground. It seems to roughly fit, but not closely enough to be conclusive and of course none of the numbers are sourced well enough for this error to be detectable in the methodology.

I could then imagine those two heights getting rounded to 309 m and 310 m respectively; or 309.6 m getting truncated to 309 m; or 306 m tallness getting rounded to 310 m; and that could explain some of the numbers I see. Converting meters to feet and back can also generate new numbers.

It's also possible that different sources are counting from different bottoms. I don't think there's a street-level entrance that would get us above 306 m, but maybe including a basement.

I wonder if plans changed during construction, reducing the intended tallness? But I can't find any evidence of that.

This article on building the Shard points out that buildings shorten during construction. It sounds like that was accounted for, but plausibly a pre-shrinking height somehow got mistaken for the finished height? (It also has a picture which makes me think that the difference between "highest floor" and "actual tip" is at least 20 m.)

And I can't rule out measurement error, either. I don't know how OS decided the tip was 308.9 m above sea level, or the aviation charts people decided it was 1,015 ft, but while I consider them fairly reliable-seeming organizations, it sure seems possible that someone misread or miscalibrated an instrument.

But ultimately I don't have a satisfying answer here, either.

  1. The main point of the article is to teach us that there's a point in London higher than the tip of the Shard. I find that mildly interesting, but not very surprising, since I'm aware of the concept of hills. But "actually this building is less tall than you think because people keep giving its height instead of its tallness" is… kinda surprising, if true, but in a not-very-surprising way. 

  2. Not the first thing I actually did, but I feel a bit embarrassed I didn't think of it sooner. 

  3. Also not actually next. 

  4. It's 22,770 posts as of December 2022. I guess the skyscraper fandom means business. 

  5. Apparently the zero point actually changed in 2016, and now things are defined to be about 25mm higher above sea level than they used to be. 

Posted on 23 June 2023

Tagged: silly

Comments elsewhere: LessWrong; /r/london