You can count Bigcommerce API calls used when working with data using dotConnect for Bigcommerce in the following way:

For SELECT statements, 1 API call is required for getting up to 250 records, so getting a thousand records consumes 4 API calls. However, please note that for complex SELECT statements that cannot be converted into Bigcommerce API calls directly, all the data from the objects, referenced by the query, is actually fetched. So in this case, API calls will be consumed for all these records, not only for records, returned by the query. You can read more about what queries can be translated into API calls directly in the SQL Translation topic.

For DML statements (INSERT/UPDATE/DELETE), 1 API call is used per 1 record.