I didn't "measure" it directly, I added it in and the pump numbers corroborated it. I'm sure it could be refined, but to what end? I would suggest a review of the calibration instructions for consistent refills, a lot easier than setting up a test rig to measure it for your specific vehicle, and you might just be overthinkin it. Or you might have peak and hold injectors too, dunno.
Mpguino calibration - EcoModder