We have a fairly extensive home auto setup at our home. Included is a Netatmo Rain Gauge. All APIed to our RaspberryPi running openhab.
One of the parameters we are able to pull from the api is accumulated rain within 24 hours, in mm.
Rather then relying on Rachios (we use their sprinkler IP bridge) "app" to schedule watering, I would rather roll our own and have more control over when the sprinklers go off.
I am not sure in mm what is considered a 'sufficient' watering for our grass. I understand this can vary, but I have no idea what a starting point would even be.