Brake Pad Life Estimator

Brake pad wear and replacement interval can be estimated from pad thickness measurements and average wear rate per mile. Most vehicles have a wear indicator that triggers a squealing sound when pads reach the minimum safe thickness, but proactive monitoring prevents the more expensive rotor damage that occurs when pads wear through completely.

Remaining brake life formula: Miles Remaining = (Current Thickness − Minimum Thickness) × Miles per mm of Wear

How this calculator gets the wear rate: Miles per mm = (Odometer now − Odometer when pads were fitted) ÷ (11 mm − Current Thickness)

Working the rate out from an assumed 11 mm new pad means you only need one measurement, which is the one most people can actually take.
If you kept an earlier reading, the sharper version is (Thickness 1 − Thickness 2) ÷ miles between the two measurements, because it does not depend on guessing what the pads started at.

Where:

• Current Thickness: measured pad thickness in mm or 32nds of an inch
• Minimum Safe Thickness: 2 mm (1/16 inch) is the absolute minimum; 3 mm is the recommended replacement threshold
• Wear Rate: typically 0.00012 to 0.00045 mm per mile depending on driving style. That corresponds to roughly 2,200 miles per mm for hard city or aggressive driving and 7,800 miles per mm for mostly-highway use, which on 9 mm of usable material works out to about 20,000 and 70,000 miles of pad life respectively
• New pad thickness: approximately 10–12 mm for most passenger vehicles

Pad thickness condition guide (mm):

• 10–12 mm: New condition
• 7–9 mm: Good (50–75% remaining)
• 4–6 mm: Moderate wear: start planning replacement
• 3 mm: Replace now: this is the recommended replacement point
• 2 mm: Replace immediately: wear indicator may be triggered
• < 2 mm: Dangerous: metal-on-metal contact possible

Driving style impact on wear rate:

• City/stop-and-go driving: 2–3× faster wear than highway
• Mountain driving (frequent downhill braking): 3–4× faster
• Aggressive/performance driving: 4–5× faster
• Highway driving: slowest wear rate

Worked example: Pads were fitted at 20,000 miles. The car now reads 55,000 miles and the thinnest pad measures 6 mm.

• Miles on these pads: 55,000 − 20,000 = 35,000 miles
• Material used: 11 − 6 = 5 mm
• Wear rate: 35,000 ÷ 5 = 7,000 miles per mm
• Down to the 2 mm hard limit: 4 × 7,000 = 28,000 miles, so around 83,000 on the odometer
• Down to the 3 mm practical threshold: 3 × 7,000 = 21,000 miles, so book the job around 76,000

7,000 miles per mm sits close to the 7,800 highway benchmark, so those pads are wearing like highway pads.
Both numbers are shown in the result, and the 3 mm figure is the one to plan around. The 2 mm limit is where you stop being safe, not where you should be aiming.