How many keywords should i use in meta tag?

If you're referring to the meta keywords tag specifically, the honest answer is that it doesn't matter how many you use, since Google and other major search engines completely ignore this tag for ranking purposes and haven't used it since 2009, so any number you choose has zero SEO impact either way. However, if you're actually asking about how many keywords to include in your meta title or meta description, which are the tags that genuinely matter for SEO, the general best practice is to focus on just one primary keyword or key phrase per page, naturally incorporated near the beginning of your meta title, rather than trying to stuff multiple different keywords into these limited character spaces. Meta titles have a practical limit of around 50 to 60 characters before getting cut off in search results, and meta descriptions typically max out around 150 to 160 characters, so there simply isn't enough room to effectively target more than one or two closely related keyword phrases without the text feeling forced, unnatural, or spammy. Prioritizing clarity and a compelling, natural-sounding description that accurately represents your page content will always outperform cramming in extra keywords, both for search engine understanding and for convincing actual humans to click through.