There is no definitive answer to how many keywords you should use on a web page, as it depends on various factors, such as the length and topic of your content, the competition and demand of your keywords, the user intent and behavior, etc. However, a general rule of thumb is to use one main keyword and a few related keywords or variations of your main keyword per web page, and to use them naturally and strategically throughout your content and site elements, without overusing or underusing them.