How to Measure Tire Tread Depth: Penny, Gauge, Methods

Why Tread Depth Matters

Tread depth is the vertical distance between the top of the tread blocks and the bottom of the main grooves. Different tire designs start with different amounts of tread, and the grooves get shallower as the tire wears. Measuring that depth is the most direct way to decide whether a tire still has useful life or needs replacement.

Federal rules for light vehicle tires define tread wear indicators as projections within the principal grooves designed to give a visual indication of the degree of wear. Those indicators are often called wear bars, and they are built into the tire, so a first check requires no tool at all.

Use the Tire's Built-in Wear Bars

Look across the main grooves of each tire. You will see small raised bars running across the bottom of the grooves at several points. As tread wears, the surface of the tire gets closer to those bars. When a bar is flush with the adjacent tread blocks, the tire has reached the low-tread point and should be replaced.

The federal standard for new non-pneumatic spare tires requires a tread wear indicator that gives a visual indication when the tire has worn to 1/16 inch. The older passenger-car standard, Standard No. 109, also requires a tread wear indicator on new pneumatic tires. The molded bars on conventional tires serve the same purpose: they make a low-tread condition visible without a gauge. See tire treadwear indicators for more.

Measure with a Tread Depth Gauge

For a precise number, use a tread depth gauge. Place the flat base on the top of the tread blocks, push the probe straight down into a groove until it touches the bottom, and read the depth. Take readings in the center of the tread and near both shoulders, because tires do not always wear evenly across the face.

Before relying on a gauge, check that it returns to zero when the probe is flush with the base. Clean the probe and keep it perpendicular to the tread surface. For more on keeping the tool reliable, see tire tread gauge calibration.

Try the Penny Test

The penny test is the common no-tool method. Hold a penny so Lincoln's head points down and insert it into a tread groove. If the top of Lincoln's head is covered by tread rubber, the tire still has some depth left. If you can see the top of his head, the tread is low and you should follow up with a gauge or the wear bars.

The penny test is a coarse pass/fail check, not an exact measurement. It can flag a very worn tire, but it cannot tell you how much tread remains. Confirm anything it tells you with a gauge before replacing tires. For wet-road and snow conditions, you may want more tread than the minimum; see tire tread depth for rain and tire tread depth for winter driving.

Where to Measure and How Often

Measure all four tires, not just the ones visible from the driver's seat. Take at least three readings on each tire: one in the outer groove, one in the center, and one in the inner groove. Repeat at several points around the circumference. The lowest reading is the one that matters, because a tire is only as good as its shallowest groove.

Uneven readings can point to a maintenance issue. If one edge is much lower than the center, under-inflation or alignment problems may be the cause. See tire tread wear causes for the common wear patterns. A periodic check, such as every oil change or before a season change, is a good way to catch wear before it becomes a safety issue.

While checking the tread, it is a good time to verify inflation. The proper cold tire pressure for your vehicle is usually found on a sticker in the driver's side door jamb or in the owner's manual; do not use the maximum pressure molded on the tire sidewall. See tire pressure basics for more.

What to Do When the Reading Is Low

The replacement threshold is not a performance recommendation. The 1/16 inch figure is the level where the tread wear indicator is set for non-pneumatic spare tires, and the molded bars on conventional tires are designed to make a similar low-tread point visible. Many drivers prefer to replace tires before the tread is that low, especially if they drive in rain or snow.

When your measurement says a tire is low, choose a replacement that fits how you drive. For daily paved-road driving, an all-season tire may be the right starting point. If you face snow and ice, consider winter tires. If you spend time off-road, look at all-terrain or mud-terrain designs. Compare options by stated specs in the all-season tires, winter tires, and all-terrain tires guides.

If all four tires are low, a matched set keeps handling consistent. Compare options in best set of four. If only two tires need replacement, choose a matched pair for the same axle with best set of two.

Compare the Measurement Methods

Each method has a place. The table below summarizes what each check tells you.

What to pick for your use

Questions

How do I measure tire tread depth with a penny?

Insert a penny into a tread groove with Lincoln's head pointing down. If the top of Lincoln's head is visible, the tread is low. The penny test is a quick pass/fail check, but a calibrated tread depth gauge gives a precise reading.

What is the minimum legal tread depth?

The federal tread wear indicator threshold used in tire standards is 1/16 inch. The molded wear bars on a tire are designed to make that low point visible, and many drivers replace tires before reaching it, especially for rain or snow driving.

Where should I put the tread depth gauge?

Place the base flat on the tread blocks, push the probe into a principal groove until it touches the bottom, and read the number. Repeat in several grooves and at multiple points around the tire, because tread wear is rarely even.

How often should I check tire tread depth?

A regular check is a good habit. Since tire pressure and tread wear are linked, checking at the same time as tire pressure, such as every oil change or before a season change, helps you catch low tread early.

Can uneven tread depth readings mean a problem?

Yes. If one side of the tire is much lower than the other, it can point to inflation, alignment, or suspension wear.

Should I replace all four tires at once?

Matching tires helps keep handling consistent, and a full set avoids differences in grip between axles. If only two tires need replacement, choose a matched pair and put them on the same axle.