They report the amount of deposits quarterly, ya goober:

> Customer deposits decreased slightly compared to Q1 to $942 million. This does not reflect the incremental deposits we received once we opened the Model 3 configurator for orders in early Q3 2018. Deposits impact the P&L only once the vehicle gets delivered to a customer.[1]

$.94 billion in deposits, where deposits are $1000 for a model 3, $20,000 for a Semi, and $250,000 for a roadster. It's also up by $90 million from two quarters before. No matter how you slice it they have a crazy number of deposits. Musk also does bring it up fairly often, certainly every earnings call that I remember.

[1]: http://ir.tesla.com/static-files/7235e525-db16-470c-8dce-9ec...