Focus distance is conventionally measured between object and sensor plane.
May I add that there should be a mark on the camera body that shows where the focal plane (sensor) is. It looks like a circle with a straight line drawn through it Φ. The line is the reference point for focus distance.
Here's a DPR photo of the Canon 60D. The focal-plane reference is a white mark to the left of the LCD:
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|Umbrellas by pleytime|
from An A to Z of Subjects- Week 21, U
|Glass ball on a perforated metal plate _2 by harubux|