PC Tires Tools

Tread Depth Calculator

How much life is left in your tires? Enter the tread depth and how far you drive, and we’ll estimate kilometres and months remaining, flag the Ontario legal minimum, and check the age.

Tread measurement

6/32″
Not sure? Leave it at the default for the tire type. It only affects the percent-worn figure.

How you drive

—usable tread left

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Tread depth
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km remaining (est.)
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months remaining (est.)

Due for tires? Shop by size or vehicle and book your install at checkout. Not sure what you’re looking at? Stop by and we’ll measure all four for free.
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Tread Depth Reference

DepthmmStatus
10–12/32"7.9–9.5New
8/32"6.4Good
6/32"4.8Fine for summer; minimum worth starting a winter on
4/32"3.2Replace soon — wet grip is going, snow grip is gone
2/32"1.6Worn out — wear bars are flush
1.5 mm1.5Ontario legal minimum (Reg. 625)
The toonie test
No gauge? Push a toonie into the tread, bear-side down. If the tread reaches the bear’s paws you’re in the top half of the tire’s life. If the tread covers only part of the silver ring, you’re roughly half worn. If you can see all of the silver and the lettering, the tire is near the end. A proper gauge costs a few dollars and takes the guessing out, or stop by and we’ll measure them.
Read it in three places
Measure the inside, centre and outside grooves on each tire and use the lowest number. Inside-edge wear with a good centre usually means alignment; centre wear means over-inflation; both edges means under-inflation. The estimate is only as good as your worst groove.

Tire Age Matters Too

Rubber hardens as it oxidizes. After about six years a tire grips noticeably less in cold and wet even with deep tread, and most manufacturers say to retire a tire at ten years from its build date no matter how it looks. The build date is the last four digits of the DOT code on the sidewall: week and year, so 3823 means the 38th week of 2023. Only one sidewall carries the full code, so you may need to look at the inside face.

Rotate every 8,000–10,000 km
On a front-wheel-drive car the fronts wear roughly twice as fast as the rears. Without rotation you end up replacing two tires early and running a mismatched set. Rotation is included with our seasonal changeover.
Check pressure monthly, cold
Southwestern Ontario swings 30°C between seasons, and pressure moves about 1 psi per 5°C. An under-inflated tire wears its shoulders and burns fuel; over-inflated wears the centre.
Replace by the worst tire
Grip is set by the weakest corner. One tire at 3/32" in a snowstorm is a problem for the whole car, and a mismatched pair across an axle upsets ABS and stability control.
Winter tires: start at 6/32"+
A winter tire below 6/32" has lost most of its sipe depth and behaves like an all-season in snow. If yours are at 5/32" in October, that’s the season to replace them, not March.

Frequently Asked Questions

What is the legal minimum tire tread depth in Ontario?
Ontario Regulation 625 under the Highway Traffic Act sets the minimum at 1.5 mm, which is just under 2/32 of an inch, for passenger vehicles and light trucks. A tire worn to its built-in wear bars is at that limit and will fail a safety inspection. Tire makers and most shops recommend replacing at 4/32" (3.2 mm) for wet-weather safety, and starting a winter with at least 6/32" on winter tires.
How many kilometres should a set of tires last?
A typical all-season tire lasts 60,000 to 100,000 km depending on the tire, the vehicle, alignment and how it is driven. Winter tires are softer and usually last 40,000 to 60,000 km of winter use. Performance summer tires can be done in 30,000 km. The most accurate estimate comes from measuring how much tread you have used over a known distance, which is what the optional kilometres-on-these-tires field does.
What does the UTQG treadwear number mean?
The treadwear grade is a relative rating set by the manufacturer under a U.S. government test: a 400 tire is expected to last about twice as long as a 200 tire from the same maker. As a rough rule of thumb, treadwear × 100 miles (× 160 km) approximates the life of the tire, so a 500 treadwear tire is in the 80,000 km range. It is not comparable across brands with any precision, which is why this tool prefers your own measured wear when you enter it.
How do I measure tread depth without a gauge?
Use a toonie. Insert it into a main groove with the bear facing down. Tread that reaches the bear’s paws means roughly half or more of the tire’s life is left; tread that only covers the silver outer band means about half worn; if all the lettering shows, the tire is near the legal limit. Measure several grooves on each tire and go by the shallowest. A $5 depth gauge is more accurate, or stop by PC Tires and we will measure all four.
How old is too old for a tire?
Most manufacturers recommend replacing tires at ten years from the date of manufacture regardless of tread, and having them inspected annually after five or six years. Find the date in the last four digits of the DOT code on the sidewall: week then year, so 3823 is the 38th week of 2023.
Do I need to replace all four tires at once?
On all-wheel-drive vehicles, usually yes: a diameter mismatch between axles can damage the centre differential or transfer case, and many manufacturers specify a maximum difference of 2/32" to 4/32" across tires. On front- or rear-wheel-drive vehicles you can replace in pairs, keeping the newer pair on the rear axle for stability.

More Tire Tools

Tire Size Calculator
Compare two sizes — diameter, sidewall, speedometer error and a fit verdict.
Plus & Minus Sizing
Going up a rim size, or down for winter steelies? Get sizes that keep your speedo honest.

Calculations use the standard metric tire-size formula (sidewall = width × aspect ÷ 100; overall diameter = rim × 25.4 + 2 × sidewall). Actual mounted dimensions vary by brand, rim width, load and pressure, typically within about 1%. These tools are a starting point, not a fitment guarantee: always confirm load index, speed rating and clearance against your vehicle's door-jamb placard and owner's manual. Questions? Call or text 519-397-4686 and we'll check it for your vehicle.

Found Your Size?

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