What is standard drinks?

Hi im confuse about it when i buy beer sometimes its 1.0 standard (4% acl 330ml beer) drinks sometimes 1.4 standard (4.8% alc 375ml beer and also 5.2% alc 330ml beer different % but still same standard drinks why is that?)drinks so what does this exactly means plus can any one tell me how many standard drinks in beer 5% 330ml?