Brake Pad Life Calculator
Enter the friction-material thickness of the pads now and when new, in millimetres, the miles driven since they were fitted, the thickness at which they count as worn out, and the price of the brake job.
Estimated miles left
16,000 mi
Estimated total pad life
36,000 mi
Usable lining left
4 mm
Share of usable lining left
44.4%
Wear per 10,000 miles
2.5 mm
Brake job cost per mile
0.83 ¢/mi
Status
Above the replacement thickness
How it works
Brake pads wear down as they are used. The lining worn so far is the thickness when new minus the thickness now, and dividing it by the miles driven gives an average wear rate. The lining still above the replacement thickness, divided by that rate, gives the miles left before the pads reach it.
The total pad life is the whole usable lining, from new down to the replacement thickness, at the same rate. Spreading the brake job's price over that life gives its cost per mile.
The replacement thickness is a figure you enter. Vehicle and pad makers publish minimum thicknesses for their parts. For comparison, the federal rule for commercial trucks and buses with hydraulic brakes, 49 CFR 393.47(d), says they "shall not be operated with a lining/pad thickness less than 1.6 mm (1/16 inch)"; that rule does not apply to private passenger cars.
Formula
wear rate = (new − current thickness) ÷ miles driven miles left = (current − replacement thickness) ÷ wear rate (0 if at or below) total life = (new − replacement thickness) ÷ wear rate cost per mile = brake job price ÷ total life
Example
Pads that were 12 mm thick when new measure 7 mm after 20,000 miles: 5 mm worn, or 2.5 mm per 10,000 miles. With 3 mm as the replacement thickness, 4 mm of usable lining is left (44.4% of the 9 mm usable when new), good for about 4 ÷ 5 × 20,000 = 16,000 more miles.
The whole 9 mm lasts 9 ÷ 5 × 20,000 = 36,000 miles, so a $300 brake job works out to 300 ÷ 36,000 = $0.0083, or 0.83¢, per mile.
Assumptions and limitations
- Wear is assumed to continue at the average rate so far. Pad wear varies with driving conditions, load and braking habits, so if those change the rate changes too; the miles left are an estimate.
- One thickness stands for the axle. Inner and outer pads, and left and right sides, can wear unevenly; the thinnest pad gives the lowest estimate.
- The new and replacement thicknesses are figures you enter; the defaults are typical, illustrative figures, not your vehicle's specification. Rotors, calipers and brake fluid are not considered, and the price is illustrative.
- This is an estimate, not a substitute for the vehicle manufacturer's service information or a brake inspection by a qualified technician.
Frequently asked questions
Is there a legal minimum brake pad thickness?
For commercial motor vehicles, the federal motor carrier safety rules in 49 CFR 393.47(d) set minimums, including 1.6 mm (1/16 inch) for hydraulic or electric brakes. Those rules apply to trucks and buses in commerce, not to private cars, whose minimums come from the vehicle or pad maker and any state inspection rules.
Why does the cost per mile use the total life, not the miles left?
The brake job pays for the whole set of pads, from new to worn out, so its cost is spread over every mile the pads last. The miles left only say how much of that life remains.
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