I am seriously baffled by most of the comments not instantly seeing the issue here given this is a networking subreddit. You do not have a 'gigabit router' you have a gigabit switch attached to a low powered network bridge in a single device. It, by its nature is a compromise as a combined device. Even the use of the word 'gigabit' for the switching portion is likely incorrect or less than what you expect if you hooked enough devices up to it and tried to transfer concurrently (backplane rate or non-blocking rate).
For the actual throughput of the WAN port on your device this would be an individually identified spec that it is capable of. The related PPS (packets per second) it can process depending on routed packet size can also be a rough way of determining this. Here is an example of Ubiquiti listing this is their model comparison for the edgerouter line of devices they sell.