Tire Tread Depth Chart: When to Replace Your Tires

Tread depth, in plain numbers

In the US, tread depth is measured in 32nds of an inch from the top of the tread to the bottom of the main grooves. Most of the world uses millimeters. The conversion is simple: divide by 32, then multiply by 25.4.

Here is the chart that matters. The two lines in bold are the ones the sources draw.

Drag the gauge to see what each depth looks like inside a groove, with the penny and quarter overlaid.

The 2/32 line: wear bars and the penny test

Every tire has a built-in warning. NHTSA describes treadwear indicators: small raised bars molded into the bottom of the grooves. When the tread wears down level with those bars, the tire is at 2/32 of an inch, and NHTSA says it's time to replace it.

You don't need a tool to spot them:

• Look across the tread for short, flat bridges running between the ribs.
• If the tread surface is flush with those bridges anywhere, you're at 2/32 there.

The coin version is the penny test. NHTSA and USTMA give the same instructions: put a penny into a groove with Lincoln's head upside down and facing you. If you can see the top of his head, the tread is at or below 2/32.

Treat 2/32 as the floor, not the goal. It's the point where the sources say you're done, not the point where it makes sense to start planning.

The 4/32 line: why rain changes the math

Tread isn't there for looks. Grooves give water somewhere to go so the rubber can stay in contact with the road. As the grooves get shallower, they move less water.

That's why AAA and Consumer Reports both draw a second line at 4/32. AAA's 2018 study, run with the Automobile Club of Southern California's Automotive Research Center, compared new all-season tires with the same tires worn to 4/32 on wet pavement:

• At 60 mph, stopping distances rose by an average of 43 percent.
• That's an extra 87 feet for a passenger car and 86 feet for a light truck.
• When the new tires had fully stopped, the worn tires were still traveling at close to 40 mph.

AAA's recommendation from that work is to replace tires at 4/32, not 2/32. The check for it is the quarter test: slip an upside-down quarter into a groove. If you can see all of Washington's head, you're at about 4/32 and it's time to start shopping.

For a South Florida driver who lives through a rainy season every year, this is the line that matters more. Our post on hydroplaning on Broward roads covers what to do in the moment.

What about Florida law?

You'll find plenty of websites quoting a specific Florida minimum tread depth. We aren't going to add another one.

We could not confirm a numeric Florida minimum against the statute text itself, so check current Florida law before relying on any number. The Florida Statutes are searchable free at the Florida Senate website (opens in a new tab). If you need a legal answer for a specific situation, ask an attorney.

Either way, the legal question and the practical one aren't the same. A tire can be over any legal minimum and still be past the point AAA recommends replacing it.

How to measure your own tires

Five minutes, and one coin or a tread depth gauge:

1. Park on level ground and turn the front wheels all the way to one side so you can see the tread.
2. Measure three grooves on each tire: the inside, the center and the outside.
3. Go by the shallowest reading. A tire is only as deep as its most worn groove.
4. Measure at more than one spot around the tire if you can roll the car a few feet.
5. Write it down for each position, so next month's reading means something.

A tread depth gauge gives you an actual number. Coins give you a pass or fail at one line. Our step-by-step penny and quarter test guide covers both methods in detail.

Uneven readings are a clue

If the inside groove reads 3/32 and the outside reads 6/32, the tire isn't just worn. Something is wearing it unevenly. Inflation, alignment and suspension are all possible causes, and new tires on the same car will wear the same way if the cause isn't found.

Extreme Tires in Sunrise does four-wheel alignments in the shop and measures tread depth at every corner during a rotation. If your readings don't match across a tire, have a technician inspect it before you buy replacements.

Depth isn't the only thing to check

A deep tread doesn't clear a tire on its own. NHTSA's inspection advice is to check the tread and sidewalls for cuts, punctures, bulges, scrapes, cracks or bumps, and to take the vehicle to a tire service professional if you see damage.

Also check the date code. A tire can have plenty of tread and still be old. Our guide on reading the tire date code shows you where to find it.

Run your readings through the Do I Need Tires Yet? check. If the answer is "consider replacing", you can shop tires by size and have them installed in Sunrise or by mobile van across Broward.