US sales - flat rate VAT scheme

Hi, I invoice both UK and USA companies. When I invoice USA - I dont need to charge VAT. If I were to join the flat rate VAt scheme- would I include the US income when calculating the gross turnover? Thank you

Invoicing USA for what? - Goods or services? If goods, sales would be exports and zero rated and zero rated counts towards gross turnover under flat rate (you'd be declaring output tax on these sales at your flat rate % even though you are zero rating the sale to the customer). If services, assuming the default rule is in play, services would be outside the scope of VAT and do not count towards gross turnover and no output tax is due on such sales. If services, be mindful of the limited cost trader rules, which will see your flat rate percentage changed to 16.5% for each VAT quarter where the limited cost trader rules are triggered.

Hi
Please refer to Notice 733 section 6 for guidance on what to include in your flat rate turnover: Flat Rate Scheme for small businesses (VAT Notice 733) 
If you are making a zero-rated supply of goods this would be included in the flat rate turnover
If you are supplying a service where the place of supply is not the UK and as such outside the scope of UK VAT this would not be included. Guidance on place of supply can be read in notice:  Place of supply of services (VAT Notice 741A)
Thank you