Brake Disc Minimum Thickness Calculator

How it is calculated

Everything is measured in millimetres. The usable wear allowance is allowance = new − minimum, the material still above the limit is remaining = max(0, current − minimum), and life % = remaining ÷ allowance × 100. The tool also reports worn = new − current. Minimum thickness is the discard figure stamped on the disc or given by the manufacturer, not a value the tool knows. Inputs are rejected when the minimum is zero or less, when the new thickness is not larger than the minimum, or when the current thickness is above the new one. A disc at or below the minimum simply shows 0 % and 0 mm, with no warning text, so read a 0 % as replace.

Common mistakes

• Typing the thickness of the disc and pad together, or the hub, instead of the disc alone measured with a micrometre across the friction surface.
• Entering a made-up minimum: the figure must come from the disc's marking or the maker's specification, because the percentage is only as good as that number.
• Reading 40 % as 40 % of the whole disc: it is 40 % of the wear allowance (new minus minimum), so only 1.2 mm of material is actually left.
• Measuring at the thickest point of a ridged disc: measure at the worn track, and take the thinnest reading.
• Treating 0 % as a reading for a disc below the limit: the tool does not show how far under you are, so check the measurement.