How to Measure Tire Tread Depth: Use a Gauge, Find the Lowest Reading and Check Winter Readiness

A tire can look healthy from the outside while one groove is much shallower than the others. A tread-depth gauge helps you find that difference—and gives you useful numbers to discuss with a tire shop instead of simply asking whether the tires look okay.

This guide covers measuring passenger-vehicle tire tread without removing a wheel. It does not certify a tire as safe, diagnose uneven wear or tell you which axle to move a tire to. Sources were checked October 31, 2026.

Start with a safe, stationary vehicle

Park on a firm, level surface away from traffic, switch the vehicle off and apply the parking brake. Use Park on an automatic; follow your owner’s manual for securing other transmissions. Do not jack the vehicle or crawl underneath it for this check. If you cannot safely reach or see the inner tread, have a tire shop complete the inspection.

Use a tread-depth gauge—not an air-pressure gauge—and read its instructions for zeroing and units. Millimetres and thirty-seconds of an inch are different scales: write down which one you are using. Keep everyone clear before any repositioning, then secure the vehicle again before measuring.

Measure the grooves, not the raised wear bars

1. Find a main tread groove. Identify the raised wear-indicator bars crossing the groove so you do not mistake one for its bottom.
2. Place the gauge probe into the groove, away from a wear bar, and seat the gauge’s base flat on the surrounding tread blocks. Read the depth using the tool’s instructions.
3. Repeat at different points across the tread and at other accessible positions around the tire. Check all four tires rather than assuming the opposite side matches.
4. Record the readings and identify the lowest measured depth for each tire. Do not average away a shallow or bald area.

The probe-and-flat-base technique comes from Michelin’s tread-check instructions. That page’s Australian legal thresholds are not Canadian rules. A raised wear bar is a separate replacement warning, not the correct place to rest the probe.

Turn the readings into a useful record

For a simple hypothetical example, readings of 6 mm, 5 mm and 3 mm across one tire leave a lowest measured depth of 3 mm. Reporting only the average—about 4.7 mm—would hide the shallow area. Those three readings do not rule out a still shallower spot elsewhere.

Label each tire by its current position: left front, right front, left rear and right rear. Record the date, odometer, units and any uneven areas. Bring the measurements to the shop; ask for the cause to be checked rather than assuming a particular alignment or suspension part needs replacement.

Wear bars and winter readiness answer different questions

Transport Canada says to replace a tire when its tread is level with the wear indicators. Do not treat remaining depth alone as approval to keep driving: cuts, cracks, bulges and other damage matter too. Suspected tire problems need expert inspection.

For snow-covered roads, Transport Canada says not to use tires worn close to 4 mm (5/32 in). That winter guidance is not the same as waiting until the wear bars are flush. A tire can still have visible grooves and be unsuitable for the snow you expect to drive through.

There is no single reading here that guarantees grip in rain, snow or ice. Use the tire manufacturer’s guidance and the applicable provincial requirements for your vehicle and season. If a reading is near a limit, repeat it carefully and have the tire assessed rather than rounding it up to justify another season.

When to stop measuring and get help

Do not continue using a visibly damaged tire simply because another groove has plenty of depth. Transport Canada identifies deep cuts, cracks, blisters and bulges as potentially dangerous. Arrange professional assistance if you find damage or cannot judge its severity; this guide is not permission to drive a damaged tire to the shop.

An even tread reading also does not replace a pressure check. Keep tread measurements and cold inflation pressures as separate maintenance records, using the vehicle’s tire-pressure instructions for the latter.