How many dollar bills are in circulation in the US?

Assumptions:

Only bills in circulation and not the ones bank's will have.

This is my thought process but if there is a better way please comment/feedback

Equation:

Avg per capita spend  * % of actual hard currency used in the transaction * Denomination split (assumption)

Avg per capita spend is 26,000$ approx. This is for the whole population

% hard currency used : I read somewhere that US predominantly uses plastic currency (cards, online, checks, stamps) and that accounts currently for 70% of the transactions

= 26,000 * 320000000 * (30/100) = 250 Billion

= Weighted split of 1$ bills, is higher as more 1$ than 10,20,100

= 30% 1$, 20% 5$ 20% 10$, 20% 20$, 10% 100$

 = 250 Billion * .30 =  75 Billion $1 Bills.