How to use the tire tread wear estimator
- Choose the unit your gauge reads: 32nds of an inch (common on US gauges) or millimeters.
- Enter an earlier tread depth, such as when the tires were new, and the tread depth now. Enter the miles between the readings.
- Enter the replacement tread depth you want to use. The starting 2/32 is an example and is not a rule for your tires or your area.
- Optionally enter the miles you drive a month. Read the miles left, the wear per 1,000 miles, the estimated full life and the months left. Use Copy, Print or CSV to keep it.
Formula
Wear = earlier reading - reading now
Wear per 1,000 miles = wear / miles between readings x 1,000
Tread left to use = reading now - replacement depth
Miles left = tread left / wear x miles between readings
This assumes tread wears at a steady rate. In practice it often wears faster as the tread gets shallow, so treat the result as a rough guide and measure again later.
8/32 now 4/32 after 20,000 miles
Say new tires measured 8/32 of an inch and now measure 4/32 after 20,000 miles. The wear is 4/32 over 20,000 miles, or 0.2/32 per 1,000 miles. If you plan to replace them at 2/32, there are 4 - 2 = 2/32 left to use.
The miles left are 2 / 4 x 20,000 = 10,000 miles. The full life from 8/32 to 2/32 would be 6 / 4 x 20,000 = 30,000 miles. At 1,000 miles a month that is 10 more months. In millimeters, a drop from 8 mm to 5 mm over 15,000 miles with a replacement depth of 2 mm leaves 15,000 miles in the same way.
Measuring tread depth
Tread depth is measured with a gauge in the grooves of the tire. Measure in several places across the width and around the circumference, and use the lowest reading, because tires often wear unevenly. Take the same readings at about the same positions each time so the comparison is fair.
Tread depth in the US is usually given in 32nds of an inch, and in many other places in millimeters. One 32nd of an inch is 0.79 mm. Pick the unit your gauge uses and keep it the same for both readings and the replacement depth.
Why this is only an estimate
A straight line is a simple model. Tire wear changes with speed, load, alignment, inflation pressure, rotation, road surface and weather, and these can change from one stretch to another. Tire age matters too: rubber hardens and cracks over the years even if the tread looks fine. A tire that is damaged or unsafe should be replaced regardless of the tread figure.
Have a tire shop measure and judge your tires. Rules and recommendations about minimum tread depth vary by place and are not built into this tool, which is why the replacement depth is an entry rather than a fixed number. See also the tire size calculator, the car maintenance schedule printable and the total cost of car ownership calculator.
Assumptions and limits
- Tread wears at a steady rate between the two readings. Real wear is often faster as tread gets shallow.
- The replacement depth is your own choice. 2/32 is an example and is not a legal limit or a recommendation.
- Both readings use the same unit and measure the same tire in the same place.
- The estimate says nothing about tire damage, age or condition. Have the tires inspected by a professional.
Frequently asked questions
How do I estimate how many miles are left on my tires?
Measure the tread twice, note the miles between the readings, and divide the tread you can still use by the tread worn so far, multiplied by those miles.
What tread depth should I replace tires at?
That is your decision together with a tire professional, based on safety, conditions and local rules. Enter the depth you want to use and the tool counts miles to it.
Why does the tool say no wear was measured?
The two readings are the same, so there is no rate to divide by. Drive more, then measure again.
Can I use millimeters?
Yes. Choose millimeters at the top and enter all three depths in millimeters.