IS 6746 provides the standard method for measuring coating thickness using magnetic gauges (DFT gauges). This is the most commonly used non-destructive method for checking paint DFT, zinc plating thickness, galvanizing thickness, and any non-magnetic coating on steel.
Method for non-destructive measurement of thickness of non-magnetic coatings on magnetic substrates (e.g., zinc, paint, chrome on steel) using magnetic gauges.
Key Values
Accuracy±5% or ±1µm (whichever is greater)
Min readings per spot5 readings averaged
CalibrationBefore each measurement session
Practical Notes
! Always calibrate the gauge on an uncoated area of the same steel substrate before measuring.
! Take minimum 5 readings per spot and average — single readings are unreliable.
! Edge effect: do not measure within 20mm of edges, holes, or corners — readings are artificially high.
! Does NOT work for magnetic coatings on magnetic substrate (e.g., steel coating on steel) — use eddy current method instead.