Because there are a lot of factors involved, you can't easily compute a flow rate. In addition to height, you need to figure resistance from going through the chiller and through all the connections, and from the pipe or tubing used.
But there is an easy way to measure your flow. Use a 1 quart or 1 gallon container, and see how long it takes to fill that container. The you can compute your actual flow rate and make any necessary adjustments.