[johnloeber]

To be clear: it's not just hard, it is explicitly wrong.

A more correct measure is a much simpler one: the aggregate product of all these companies over the GDP. Note that this aggregate product is of course a component of the GDP, so you can express this neatly as a percentage. I see only one major accounting complication in constructing this metric, and that's the inclusion/exclusion of foreign products and subsidiaries. (See e.g. offshore revenues that are not repatriated, and therefore not part of the domestic product calculations -- I think?)

[ThrustVectoring]

Another way is to estimate the net present value of America's GDP by multiplying it by 20 or so, which implies that it's roughly 1% of American wealth.

Alternatively, percentage of rents at office and industrial zoned land would be a good measure. That'd separate out national vs international activity, at the cost of being significantly more difficult to estimate and calculate. I actually don't know how well rents and imputed rents are tracked at aggregate levels and broken down by company, so this may very well be data that we simply don't have access to.

[jklein11]

Out of curiosity, why ~20?

[quantumhobbit]

P/E ratios are around 20 on average I suppose. Meaning earnings are 5% of the market cap of a stock.

GDP doesn't directly correlate to earnings though.

[ThrustVectoring]

Historically, $20 is the price of something that gives you $1/year. This, like, goes back to the medieval era.

[arjunnarayan]

It's just a rule of thumb as to what long run P/E ratios look like in the equity markets.

[donaldguy]

Are product numbers (domestic or multimarket) accessible somewhere to construct this? (Would revenue numbers suffice or is there more that should be factored in?)

Or is there an accepted measure of national economy that might play a sensible denominator for the sum I put together?

As I said, I don't know enough about economics to pretend to be making a reasonable comparison, I just went for the numbers I could find on a whim at 2am :-)

Thanks for actually knowing things

[foota]

Could look at the GNI, gross national income. It's gdp plus net foreign income