Published by Rims & Tires
Compiled & checked by the site's publisher from manufacturer, NHTSA & USTMA data · Updated 2026-08-12
Put a penny into a tread groove with Lincoln's head pointing down. See the top of his head and the tire is at or below 2/32" — legally worn out. Repeat with a quarter: see the top of Washington's head and you're at or below 4/32", the depth most safety-minded drivers replace at. The whole check takes about a minute per tire and needs nothing but pocket change.
How does the penny test work (2/32")?
Insert a penny into the tread groove with Lincoln's head pointing down. If you can see the top of Lincoln's head, your tread is at or below 2/32" — the tire is legally worn out and must be replaced immediately.
At 2/32" the tire has lost most of its ability to evacuate water in wet conditions. Wet stopping distances increase dramatically and hydroplaning risk is very high. The U.S. Tire Manufacturers Association uses the same threshold: once tread wears down to 2/32 of an inch, it's time to visit a tire shop.
How does the quarter test work (4/32")?
Insert a quarter with Washington's head pointing down. If you can see the top of Washington's head, tread is at 4/32" or below — replace the tires before winter weather or any significant rain driving.
At 4/32" wet-weather grip has declined noticeably but the tire still handles dry conditions acceptably. Most safety-conscious drivers use 4/32" as their replacement threshold.
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What are tread wear indicator bars?
Modern tires have built-in tread wear indicators: small raised bars molded into the tread grooves at 2/32". When the tire surface is flush with those bars, the tire is at the legal wear limit. No penny needed.
Look for a small triangle or "TWI" marking on the tire sidewall. Those point to where the wear indicator bars sit in the grooves.
Where on the tire should you check tread depth?
Check the center of the tread AND both outer edges. Center-only wear = over-inflation. Edge wear = under-inflation or alignment issue. Even if the center looks fine, edge wear means the tire life is compromised.
Also check all four tires. Uneven tread depth across axles can indicate rotation was skipped — and can stress AWD drivetrains if the circumference difference is large enough.
Frequently asked
How often should I check tire tread depth?
Every tire rotation (every 5,000–7,000 miles) is a natural time to check. Also check before a long road trip and before winter.
What's the minimum legal tire tread depth?
2/32" is the most common statutory minimum and the threshold most states use — it's Georgia's legal minimum under O.C.G.A. § 40-8-74, and it matches the federal tread-depth floor used in commercial vehicle inspection criteria (49 CFR § 393.75). It is not universal: a small number of states set a different number or have no statutory tread-depth minimum at all, so if you're outside Georgia, it's worth a quick check of your own state's rule. Most safety organizations recommend replacing at 4/32" — especially if you drive in rain.
How deep is the tread on a new tire?
Most new passenger tires start at 10/32" to 11/32". Winter tires often start deeper, around 12/32", and high-performance summer tires can start as shallow as 8/32". Knowing your starting depth is what turns a gauge reading into something useful — it tells you how much of the tire's usable life is actually left, not just whether it has passed the legal limit.
Can I buy a tread depth gauge?
Yes — they cost $3–10 at any auto parts store and give you a precise reading in 32nds of an inch. More accurate than the penny test for borderline tires. Push the base flat against the tread surface with the probe down in the groove, and take readings at the inner edge, the center, and the outer edge rather than one spot.
Is the penny test actually accurate?
Accurate enough to catch a bald tire, not precise enough to judge a borderline one. A penny only answers yes or no at 2/32", and a quarter only at 4/32". If you want to know whether you have 5/32" or 7/32" left — the difference between shopping now and shopping next spring — spend the few dollars on a tread depth gauge or ask a shop to measure it.
Why is one of my tires more worn than the others?
A little variation is normal, but a big gap usually means a skipped rotation, an alignment issue, or one tire running low on air. Fix the cause before you just swap the worn tire, or the new one wears the same way. A shop can pin down what is actually driving it.
Does tread depth really matter if my tires still look fine?
It matters more than looks. A tire can have plenty of rubber left and still be worn down in the grooves that handle rain, which is exactly where a worn tire gets dangerous. The check takes a minute and tells you what your eyes cannot.
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Last updated 2026-08-12. General guidance only — confirm specifics with a local shop for your exact vehicle.