Use a tread depth gauge and place it in the tread groove
Press the gauge base flat against the tire tread
Read the measurement in 32nds of an inch or millimeters
Check multiple spots across each tire
Look for the wear bars built into the tread
If the tread is level with the wear bars, the tire is worn out
Use a penny test by inserting a penny into the tread with Lincoln’s head down
If the top of Lincoln’s head is visible, the tread is too low
Repeat on all four tires
Compare the readings to the tire manufacturer’s recommended minimum depth