Systems and methods are provided for measuring depth, position, and/or angle of a cannula in a medical drug delivery device. In particular, a drug delivery device having a cannula is positioned adjacent to tissue, a voltage pulse is provided to the cannula, a charge is measured at an electrode in the drug delivery device, and the depth of penetration of the cannula is determined based in part on the charge at the first electrode. Systems and methods described herein can be used to determine subcutaneous insertion depth in a wearable bolus injector. In some implementations, insertion depth determination is achieved through capacitive sensors which measure needle depth in a drug delivery device.