The US does not look for specific grades in certain subjects as in the UK. They will expect you to have graduated with a high school diploma (in the UK, completed a 2 year post GCSE qualification to a minimum pass grade, with passes in GCSES as appropriate) and they will look at your overall GPA or equivalent, as well as your SAT/ACT scores and admission essays etc.
You may find not all universities will accept a BTEC, as they are fundamentally vocational qualifications, particularly the top tier universities who tend to prefer students with rigorous academic profiles (e.g. IB/A-level with high marks).
Your best bet is to contact the relevant admissions teams at the universities you're looking at and ask them if they accept it as an entry qualification. You may be able to find a GPA conversion chart somewhere but I would just ask them admit teams, as they'll be the ones with the last word anyway, and will know better than random people on the internet.