Yes, google maps is free to use. If you are using google maps for standard use for navigation on your mobile phone or viewing online maps… But if you are developer and you want to include google maps in your program with API you must pay a fee per 1000 requests.
Example: if you use Place Details API call you will pay $17 per 1000 requests. But there is a good side of using google maps API every month you get $200 FREE credit from google for using there API. Basically, unless you use google maps a lot you use will be totally FREE.
Mora about pricing for google maps API check on website: https://cloud.google.com/maps-platform/pricing/