The number of API requests that people need to make of a zip code API can fluctuate a lot. Some prospective users have questions about the API request limit on the Plans page. The page shows the requests per minute limit but the only limit that matters is the numbers of requests per hour. So your request number can fluctuate as much as you want as long as you stay below the hourly limit.
The per minute limit is there strictly for informational purposes only. API requests sent over the hourly limit will not receive the expected response.
You can try ZipCodeAPI and get 10 API requests per hour for free forever. And for the first two weeks, you will get 50 requests per hours as part of your free trial. Then if you need more than 10 requests per hour, you can decide what is the right amount for you.