The "penny test" is a quick way to estimate whether your tire tread is worn down to the legal minimum in the United States.
Here's how it works:
- Insert a U.S. penny into a tread groove with Abraham Lincoln's head pointing downward.
- If the top of Lincoln's head is completely visible, the tread is less than 2/32 inch (1.6 mm) deep.
- If part of his head is covered by the tread, you have more than 2/32 inch remaining.
Is it still accurate?
Yes—but with an important caveat.
The penny test is still accurate for determining whether a tire has reached the U.S. legal minimum tread depth of 2/32 inch. It hasn't become obsolete because modern tires are different.
However, many tire safety experts and tire manufacturers recommend replacing tires before they reach 2/32 inch because wet-weather performance declines well before then.
A common guideline is:
- 6/32 inch: Consider replacing tires if you frequently drive in heavy rain. Hydroplaning resistance starts to decrease noticeably.
- 4/32 inch: Replace tires if you regularly drive on wet roads. Stopping distances in the rain increase significantly.
- 2/32 inch: Legal minimum in most U.S. states for passenger vehicles. Tires at this depth have greatly reduced traction, especially on wet roads.
Better alternatives
Modern methods are generally more informative:
- Built-in tread wear indicators: Most tires have small raised bars molded into the grooves. When the tread becomes flush with these bars, the tire is at approximately 2/32 inch and should be replaced.
- Tread depth gauge: An inexpensive gauge provides an exact measurement in 32nds of an inch or millimeters.
- Quarter test: Some people use a U.S. quarter as a rough indicator for about 4/32 inch, which is a more conservative threshold for wet-weather safety.
Bottom line
The penny test is still a valid way to check whether a tire has reached the legal minimum tread depth. But if you're concerned about optimal safety—especially in rain or snow—a tread depth gauge and replacing tires before they reach 2/32 inch provide a better margin of safety.
