Selon Google à compter de janvier 2016, la limite gratuite est de 100 000 requêtes par jour.
Voici l'url précise ainsi que le texte original de google :
Shared* daily free quota of 100,000 requests per 24 hours; additional requests applied against the annual purchase of Maps APIs Credits. Maximum of 23 waypoints per request. Rate limit applied per user session, regardless of how many users share an IP address.**