Tire tread depth

Bridgestone says tire tread depth in the United States is measured in 32nds of an inch. It says tread depth gauges should read in both 32nds and millimeters. The nominal metric equivalents are 1.6 mm for 2/32 in and 3.2 mm for 4/32 in.

Bridgestone says new tires typically have 10/32 in or 11/32 in of tread. New-tire depth varies by model, so the maker’s size table is the reference for a particular tire. The Toyo, Nitto, and Firestone size tables checked October 15, 2026, list these examples for LT265/70R17.

• Toyo lists 16.3/32 in for the Open Country A/T III.
• Nitto lists 16.4/32 in for the Ridge Grappler.
• Firestone lists 18/32 in for the Winterforce LT.

For the penny test, NHTSA says to place a penny in the tread with Lincoln’s head upside down and facing you. If the top of his head is visible, NHTSA says to replace the tire. Goodyear describes seeing all of Lincoln’s head as indicating less than 2/32 in of tread.

For the quarter test, Goodyear says to insert a quarter into a tread groove. If the tread touches Washington’s head, Goodyear says at least 4/32 in remains. The quarter test checks a different depth from the penny test.

Bridgestone says to check each tire and various places around each tire when using the penny test. It says to replace a tire when any area fails, even if other areas have more than 2/32 in remaining. Goodyear also identifies a tread depth gauge and built-in wear indicators as ways to check tread.

NHTSA describes treadwear indicators as raised sections between the tread. Under 49 CFR 571.139 (FMVSS No. 139), passenger and LT radial tires must have at least six indicators spaced approximately equally around the circumference. They show when tread has worn to 1/16 in, equivalent to 2/32 in.

NHTSA says to replace tires when the tread is level with those indicators. The bars mark the replacement depth; they do not show that a tire retains its earlier wet-weather performance. Bridgestone warns that performance can diminish significantly before tread reaches 2/32 in.

For vehicles subject to FMCSA’s 49 CFR 393.75, front tires on buses, trucks, and truck-tractors must have at least 4/32 in in a major tread groove. Other tires on those vehicles must have at least 2/32 in in a major tread groove. These are federal motor-carrier requirements, not a statement of state passenger-car minimums.

NHTSA says tires are not safe and should be replaced when tread is worn down to 2/32 in. Goodyear also says to replace tires at 2/32 in or less. NHTSA advises checking tread at least once a month.

Do not treat the replacement depth as a wet-weather performance guarantee. Bridgestone says tires meeting the minimum legal requirement may still hydroplane or lose control in rain or slush. NHTSA says winter tires are more effective than all-season tires in deep snow.

Tread depth is not the only replacement consideration. NHTSA notes that some vehicle and tire manufacturers recommend replacement at six to 10 years old regardless of treadwear. The tire date code helps identify tire age.