TireGeoCalcHow Much Tire Tread Is Too Little?
Tire tread is considered too little at 2/32 of an inch according to NHTSA guidelines.
At 2/32 of an inch (1.6 mm), tires reach the standard replacement threshold.
However, testing reported by Tire Review shows that wet stopping distance is much longer at 4/32 of an inch (3.2 mm) and longer again at 2/32.
For rainy conditions, Tire Review recommends replacing tires at 4/32 of an inch.
Understanding tire tread depth measurements
Tread depth is measured in thirty-seconds of an inch in the United States and in millimeters internationally.
According to Cars.com, new passenger car tires typically begin with 10/32 of an inch to 11/32 of an inch of tread.
In millimeters, 10/32 of an inch is 7.9 mm (converted: 1 inch = 25.4 mm).
11/32 of an inch is 8.7 mm.
Check original tire dimensions using our guide on how to read a tire sidewall.
Wet stopping distance test results
A test by Tire Rack, reported by Tire Review, shows how stopping distance grows as tread wears down.
In that test, a car on new tires stopped in 195 ft according to Tire Review.
With tread worn to 4/32 of an inch, the same car needed 290 ft according to Tire Review.
4/32 of an inch is 3.2 mm.
When worn to 2/32 of an inch, the car needed 379 ft to stop according to Tire Review.
Tire Review also reported that the car on 2/32 tires was still moving at 44 mph at the point where the car on 4/32 tires had stopped.
For snow driving, Tire Review recommends 6/32 of an inch (4.8 mm) before winter starts.
Tread depth benchmarks and guidelines
The table below summarizes tread depth benchmarks, metric conversions, and industry recommendations.
| Tread depth (32nds) | Metric depth | Condition and guideline | Cited source |
|---|---|---|---|
| 10/32 to 11/32 in | 7.9 mm to 8.7 mm (calculated) | Typical depth for new passenger tires | Cars.com |
| 6/32 in | 4.8 mm (calculated) | Recommended threshold for snow tires | Tire Review |
| 4/32 in | 3.2 mm (calculated) | Recommended wet threshold; tested with a 25-cent coin | Tire Review, Michelin |
| 2/32 in | 1.6 mm (calculated) | Standard replacement point; tested with a 1-cent coin | NHTSA, Michelin, Cars.com |
Calculated dimensions
- Tread depth (32nds)
- 10/32 to 11/32 in
- Metric depth
- 7.9 mm to 8.7 mm (calculated)
- Condition and guideline
- Typical depth for new passenger tires
- Cited source
- Cars.com
- Tread depth (32nds)
- 6/32 in
- Metric depth
- 4.8 mm (calculated)
- Condition and guideline
- Recommended threshold for snow tires
- Cited source
- Tire Review
- Tread depth (32nds)
- 4/32 in
- Metric depth
- 3.2 mm (calculated)
- Condition and guideline
- Recommended wet threshold; tested with a 25-cent coin
- Cited source
- Tire Review, Michelin
- Tread depth (32nds)
- 2/32 in
- Metric depth
- 1.6 mm (calculated)
- Condition and guideline
- Standard replacement point; tested with a 1-cent coin
- Cited source
- NHTSA, Michelin, Cars.com
Millimeter values are converted from inches (1 inch = 25.4 mm). Michelin publishes 1.6 mm for the 2/32 mark.
How to check tire tread depth step by step
You can check remaining tread depth with coins or built-in indicators using these steps:
- Park on level ground: Turn wheels outward to inspect the tread face clearly.
- Perform the 1-cent coin test: Place a 1-cent coin into a groove, as described by NHTSA.
- Inspect Lincoln's head: NHTSA says to replace the tire if you can see Lincoln's head.
- Perform the 25-cent coin test: Place a 25-cent coin into the tread, as described by Tire Review.
- Read the result: Tire Review ties the 25-cent coin test to the 4/32 mark, the level it recommends for rainy climates.
- Examine wear indicator bars: Cars.com explains that molded bars sit at 2/32 of an inch in 4 equidistant locations.
Legal minimums versus practical recommendations
Michelin and Tire Review note that driving on tires below 2/32 of an inch is illegal in some US states. Check the rule in your state.
According to Michelin, 2/32 of an inch (1.6 mm) represents the legal minimum threshold.
However, Michelin emphasizes that wet braking grip drops noticeably at 4/32 of an inch (3.2 mm).
In dry climates like Arizona, Tire Review notes that 2/32 of an inch may be sufficient.
Check your vehicle door placard or owner's manual for proper tire specifications.
Inspect pre-owned tires before purchasing with our used tire check resource.
To compare replacement sizes, test dimensions in our tire size calculator and tire size alternatives tool.
Frequently asked questions
When should you replace tires based on tread depth?
NHTSA and Michelin define 2/32 of an inch (1.6 mm) as the standard replacement threshold.
However, Tire Review test data shows wet stopping distance reached 379 ft at 2/32 of an inch.
At 4/32 of an inch, stopping distance was 290 ft according to Tire Review.
How do you test tread depth with coins?
Place a 1-cent coin into tread: NHTSA says to replace the tire if you can see Lincoln's head.
Place a 25-cent coin into tread: Tire Review uses this test for the 4/32 mark, the level it recommends for rainy climates.
Where are tread wear indicator bars located?
According to Cars.com, wear bars are molded at 2/32 of an inch across 4 equidistant locations around the tire circumference.
NHTSA and Michelin both give 2/32 of an inch as the replacement point, so a tire worn down to the bars is due for replacement.