Tire tread life calculator

What tread depth tells you

Tread grooves carry water and snow away from the contact patch, so as they get shallower the tire grips less in the wet and in snow. A projection of wear, built from your own measurements, is more useful than the treadwear number on the sidewall, which only ranks tires against each other. This page turns two readings and the miles between them into a replacement date.

The method

Wear rate = (depth when new − depth now) ÷ miles driven on the tire. Miles left = (depth now − limit) ÷ wear rate. Months left = miles left ÷ miles per month. It is a straight-line projection: it assumes the next mile wears the tire as much as the average of the past ones. Depth is taken in 32nds of an inch, the U.S. unit, or in millimeters.

Worked examples

A tire that started at 10/32 and now measures 6/32 after 20,000 miles has lost 4/32. The wear rate is 2.0/32 per 10,000 miles, so the whole usable life to 2/32 is 40,000 miles, of which 50 percent has gone. At 1,000 miles a month, 20 months remain to 2/32, 10 to 4/32 and 5 to 5/32. For a faster case, a set at 7/32 after 9,000 miles (3/32 lost) has 9,000 miles left to 4/32, or 6.0 months at 1,500 miles a month.

Common mistakes

Measuring in one groove only gives the best-looking number: the shoulders usually wear first, so measure across the width and use the lowest reading. Using the wrong starting depth is the second mistake. The tread depth of a new tire varies by model and type and the maker's specification, or a measurement of an unworn tire of the same type, is the value to use; we do not assume one. The third is a short baseline: with less than about 5,000 miles of wear the measuring error of a hand gauge is a large share of the loss, so the projection is unreliable. Finally, rotating tires moves them between positions: measure the depth at each position, and use the highest wear rate.

Limits of this method

Tread does not wear in a straight line. Seasonal use, load, inflation and alignment all change the rate over a tire's life. Tire age is separate from tread: rubber ages even when unused, so a tire with plenty of tread can still be unsafe, and the maker's age guidance and the tire's DOT date code apply. Tread depth is one of several factors in grip on wet roads; the condition of the tire, its inflation and speed also matter. This calculator tells you when your tread reaches a number; it does not say whether the tire is safe to drive. When in doubt, have a tire professional inspect it.

How do I work out how many miles my tires have left?

Subtract the current tread depth from the depth when new to get the wear so far, divide by the miles driven to get the wear rate, then divide the tread above your replacement limit by that rate. A tire that started at 10/32 inch and is now at 6/32 after 20,000 miles has lost 4/32, a rate of 2.0/32 per 10,000 miles. To the 2/32 legal minimum it has 20,000 miles left; to the 4/32 many shops advise it has 10,000; to the 5/32 suggested for snow, 5,000.

What is the legal minimum tread depth?

Tread depth is measured in 32nds of an inch in the U.S., and most states set the legal minimum at 2/32 inch (1.6 mm). Federal tire standard FMVSS 109 requires tread wear indicators that show 1/16 inch (the same depth) as a visual signal; it does not itself set a limit for how deep your tread must be. Check your own state's vehicle code: we could not open a national list. Rules for commercial vehicles are separate.

Is 2/32 inch really the time to replace tires?

It is the point where the law and the wear bars say stop, not where the tire is still doing its job. Tire Rack advises replacing at about 4/32 inch for wet roads and about 5/32 inch for snow, and reports that tires at 2/32 needed roughly 100 more feet to stop in its wet testing than tires at 4/32. Michelin, as reported by trade press, treats 2/32 as the minimum allowable depth. The calculator lets you pick any of the three limits and shows all three.

How does the penny test work?

Put a penny into a groove with Lincoln's head upside down and toward the tread. If the top of the head is fully visible, the tread is at or below about 2/32 inch. The quarter test is used the same way for 4/32 inch, with Washington's head. A gauge is more accurate and cheap, and you should measure in several grooves across the tire, since the edges often wear faster than the center.

What does the UTQG treadwear number mean?

It is a number on the sidewall set by the tire maker, reflecting a comparison with control tires run on a government test course near San Angelo, Texas (49 CFR 575.104). The regulation's own example: a tire graded 150 would wear one and one-half times as well on that course as a tire graded 100. The rule also says the relative performance depends on the actual conditions of use. So the number ranks tires of the same maker's grading, but it is not a mileage promise, and you should not convert it into miles with a fixed factor.

Why do my tires wear faster than the number suggests?

Under-inflation, misalignment, hard braking and cornering, heavy loads, hot pavement and no rotation all raise the rate. Uneven wear is the clue: wear on both edges points to low pressure, wear on the center to too much, and wear on one edge to alignment. Fix the cause before you trust the projection.

Can I take wear in millimeters?

Yes: pick millimeters in the depth unit. One 32nd of an inch is 0.794 mm, so the 2/32 limit is 1.6 mm, 4/32 is 3.2 mm and 5/32 about 4.0 mm.

Safety information, not a substitute for a tire inspection by a professional or for your vehicle’s owner’s manual. Sources: 49 CFR 571.109 (FMVSS 109), S4.2.1: tread wear indicators for 1/16 inch; 49 CFR 575.104 (Uniform Tire Quality Grading), treadwear grade, control tires, course in Texas, and the 150 versus 100 example (eCFR, read October 28, 2026). The 4/32 and 5/32 thresholds are Tire Rack’s advice (tirerack.com, a tire retailer, so a vendor source). The 2/32 state minimum and the penny and quarter tests are reported by trade and consumer publications (Tire Review, Consumer Reports); we could not open the NHTSA tire pages. Related: tire size calculator, tire load index calculator, stopping distance calculator. How we check our calculators.