That’s a weird way to account for their business size. There isn’t a significant marginal cost per transaction. They didn’t sell $12T in products. They facilitated that much in payments. Their profits are fantastic.

If you have no clue how profit margins are calculated then you're better off staying quiet.

It's quite simple. Divide revenue minus costs by revenue. Transaction volume isn't revenue. Visa only gets the transaction fee.

Even if I give you the benefit of the doubt and do a proper interpretation of the number you've arrived at, its meaning is quite different and quite off topic from this discussion. What you have calculated is the total share of costs that Visa represents in that 12 trillion dollar part of the economy. It is like saying Visa's share of GDP is 0.1%.

I didn't say that was their profit margin, that's their transaction margin.

As my mother used to say if you have nothing nice to say you're better off staying quiet ;)