According to our company policy, each product has its own limitations (unless otherwise agreed upon individually).
For example, using the Real-time Distance Matrix API with traffic conditions, you can send a request with no more than 100 elements at a time. These can be matrices of 1x100, 10x10, 5x20, etc.
The Asynchronous Distance Matrix API with traffic conditions has no limit in the request size, but daily usage should not exceed 80,000 elements. For example, no more than 10 queries for 20x400 matrices (10 * 20 * 400 = 80,000) per day.