How much/How many means“多少”in Chinese, please remember that there is only one 多少 in Chinese，多 means more and 少 means less，no matter something is countable or uncountable, all things can be measured, more or less.
多少? can be used independently to ask How much or How many of something, let’s take a look at an example below:
A：老板，我想买点米。
B：要多少？
A：5斤吧。
多少 is usually used with a measure word or you can say quantity word, like 个，斤，张，etc., for example:
A：你要多少斤米？。
B：5斤吧。
几 refers to a countable number of something.it means How many. for example:
1，if 几+measure word， usually 几 indicates a number less than 10，
A：你有几个姐姐？
B：只有一个。
2，1加1等于几？（1 plus 1 equals 几?.）
both 几 and 多少 could be used with measure words. for example:
A：你要几（多少）斤米？
B：5斤吧。