How to replace an odd-size (2 1/4" x 1 7/8") downspout elbow?

Question

An elbow in one of my downspouts is broken and I want to replace it. But the downspout's measurements are 2 1/4" x 1 7/8" which is different from the standard sizes in USA which are 2" x 3" inches or 3" x 4".

Are there replacement parts available for 2 1/4" x 1 7/8" downspouts, and if so where? I couldn't find anything useful on Google, Home Depot, Amazon, etc. but might not be looking for the correct keywords. Is there a name for this size that isn't the actual dimensions, like how a wood "2x4" isn't really 2 inches by 4 inches?

If replacement parts aren't available, then how should I replace this odd-size downspout elbow without having to replace the entire downspout? (The downspout goes up 3 stories so would be a pain to replace-- and only the detachable elbow at the bottom has a problem.) This downspout is in an out-of-the-way corner of our back yard so I don't care about appearance. In other words, it's OK if the fix is kinda ugly as long as it won't leak.

Here's what it looks like now:

Answer 1

The good news is that your down spout is a simple, plain rectangle tube -- no fancy profile rolled into it as is common with most down spouts.

That's good news because it means you can easily have a new part made. If you want to bang it out yourself you can find rolls of pre-painted "aluminum trim coil" in a range of colors at home centers. First find a large sheet of paper or thin cardboard such as a breakfast cereal box. Work out how to make a series of cuts and folds to form the part you need. You'll have to find edges you can bend the sheet around. The jaw of a vise, the corner or edge of a table, a cut piece of wood -- be creative as you search for objects to help with the forming. You may be able to form the aluminum with your hands, but will probably need to strike it with a hard rubber or urethane hammer to get the bends sharp enough.

Or, if you don't want to earn the Down Spout Making merit badge, find a local contractor who does siding, trim, fascia, gutters, etc. They'll have material in stock as well as tools and machinery for forming custom parts like this. They do it all the time. You could bring them the broken elbow, and maybe a section of the down spout, so that they can custom-make a replacement that fits just right.

Answer 2

You guessed correctly that downspouts are sometimes sized like wood - there is a "nominal" size which is how they are described, and an "actual" size which is the true measurements. According to GutterSupply.com (chart 1-3), 2x3 and 3x4 downspouts (and also 4x6) have nominal and actual numbers that are the same¹, but for other sizes they are not. Here is the relevant portion of their chart:

+--------------+-------------+
| Nominal Size | Actual Size |
+--------------+-------------+
|            2 | 1.75 x 2.25 |
|            3 | 2 x 3       |
|            4 | 3 x 4       |
|            5 | 3.75 x 4.75 |
|            6 | 4 x 6       |
+--------------+-------------+

Based on this chart, your downspout is very close to their "standard" "2-inch" size. That said, as you seem to have found, it's going to be very hard to find this size in any store (GutterSupply.com which has the chart that identifies it doesn't even sell it). Greg Hill's answer has the information you need about getting custom replacements.

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1: Note that others disagree about the sizing of the other "standard" sizes. For example, this supplier says that 2x3 is actually 2.25x3.125, 3x4 is actually 2.938x4.25, and 4x5 is actually 3.75x5.375.