There isn't necessarily an ideal length for a meta tag, as the appropriate length can vary depending on the specific type of meta tag and its purpose.
For example, the ideal length for a meta title tag is generally considered to be between 50-60 characters, as this is the typical maximum number of characters that search engines will display in search results. However, the length of a meta description tag can vary and can be up to around 155-160 characters, as this is the typical maximum number of characters that search engines will display in the description snippet in search results.
It's important to note that while there are general guidelines for meta tag lengths, it's more important to focus on creating accurate and relevant meta tags that provide clear and concise information about the content on the page.