The prospectus for all three issues (2018,2019,2021) require the principal amount to be paid in cash
$426 million in face value noticed early conversion after 6/30/16. Assuming the VWAP for those conversions(each holder could have given notice on a different dates causing a slightly different VWAP) was $225 (predominate price in August):
-the first $124.52 of the VWAP was settled by Tesla in cash
-the IB hedge writers were responsible for the next ~$60 of the VWAP ($184.48-$124.52) (it's unclear how this was settled).
-this leaves $40,52 to be settled at Tesla's option in either cash or shares.
The share equivalent of the $426 million in face value would be (426/660) x 5.3 million = 3.42 million shares
So if only the un-hedged portion was paid in shares (and the newly issued shares were at the VWAP) : ($40.52/$225) x 3.42 million = 615,900 shares.
Note: the 10Q on August 5, 2016 said a cumulative $411m million of face value had been noticed for conversion. Approximately $14 million of that was prior to 6/30/16, leaving $397 million being noticed between 6/30/16 and 8/5/16, and apparently another $15 million in face value of new notices between 8/5/16 and 8/31/16. If one were to use either alternate amounts of face value, the additional shares would calculate as:
$397 million = 574,000 shares
$411 million = 594,000 shares
The VWAP and the stock price on the date(s) the shares were distributed to the noticing note holders also affect the calculation of the number of new shares issued. The IB hedge writers could have settled their middle layer in cash or previously-issued shares already counted in shares outstanding (from their own internal hedging). The maximum number of new shares for the early conversion notices received thus far is about 1.5 million, assuming the IB hedge writers settled with Tesla for cash and Tesla uses shares to settle with note holders for everything above par.