Tread Depth Calculator - Remaining Tire Life & Replacement Date

New tire vs yours - what 3 mm actually means

A brand-new summer tire ships with 8 mm of tread. At 3 mm, braking distance on wet roads increases by 30-40% compared to new. At the legal minimum of 1.6 mm, it nearly doubles. This calculator takes your current tread measurement and tells you exactly where you stand: wear percentage, estimated kilometers remaining, months until replacement, and whether your tread is wearing evenly or flagging an alignment problem.

How to measure and calculate - step by step

Tire type - select summer, winter or all-season. This sets the factory depth and recommended replacement threshold (3 mm for summer/all-season, 4 mm for winter).
Tread depth (mm) - measure in the main groove with a tread depth gauge, caliper, or coin. For the quarter test: if Washington's head is fully visible, you are at about 4 mm. Lincoln penny: about 2 mm.
Edge depth (optional) - measure the shallowest point on the inner or outer edge. If it differs from center by more than 0.5 mm, the calculator flags uneven wear and diagnoses the likely cause.
Annual mileage - enter your yearly driving distance. The calculator divides remaining tread by your wear rate to estimate months until replacement.
Read the results - wear percentage, remaining km, replacement date, visual bar, limits table, and any uneven wear alerts.

Before and after - what changes as tread wears

BEFORE (new tire, 8 mm)

Wet braking 60-0 km/h: 18 m
Aquaplaning speed: 85+ km/h
Snow grip: 100% (winter tire)
Remaining life: 32,000-40,000 km
Legal status: fully legal

AFTER (worn tire, 2 mm)

Wet braking 60-0 km/h: 28 m (+55%)
Aquaplaning speed: 55 km/h (-35%)
Snow grip: 40% (winter tire)
Remaining life: 2,000-3,000 km
Legal status: borderline

Tread depth reference table

Depth	Status	Wet braking penalty	Action
8 mm	New	0%	None needed
6 mm	Good	+5-10%	Monitor
4 mm	Acceptable	+15-25%	Replace winter tires
3 mm	Schedule replacement	+30-40%	Replace all tires
2 mm	Critical	+50-60%	Replace immediately
1.6 mm	Legal limit	+80-100%	Illegal below this

Practical examples

Example 1: Summer tire, 5.2 mm center, 15,000 km/year.
Result: 44% worn, 14,300 km to recommended limit (3 mm), about 11 months remaining.

Example 2: Winter tire, 4.5 mm center, 3.0 mm edge, 12,000 km/year.
Result: 58% worn, edge 1.5 mm below recommended. Uneven wear alert: check alignment. Replace soon.

Example 3: All-season tire, 2.0 mm, 20,000 km/year.
Result: 94% worn, 2,200 km to legal limit. Status: critically worn - replace immediately.

Example 4: Summer tire, 7.5 mm, 8,000 km/year (city driver).
Result: 8% worn, 29,250 km to recommended limit. Near-new tire - 44 months of driving remaining.

Example 5: Winter tire, 6.0 mm center, 6.5 mm edge, 25,000 km/year (commuter).
Result: 36% worn, center more worn than edge (overinflation), 10,000 km to 4 mm winter limit, about 5 months.

FAQ - Frequently asked questions

What is the legal minimum tread depth?

In the US, most states require 2/32 inch (1.6 mm). The EU standard is also 1.6 mm. However, tire safety experts and organizations like NHTSA and TUV recommend replacing tires at 3 mm for summer and 4 mm for winter tires, because grip drops significantly below these thresholds - especially on wet or snowy roads.

How do I measure tread depth without a gauge?

In the US, use the quarter test: insert a quarter head-first into the tread groove. If you can see the top of Washington's head, you have less than 4 mm (4/32 inch). The penny test: if Lincoln's head is fully visible, you are at about 2 mm (2/32 inch) - replace the tire. In Europe, insert a 1 or 2 euro coin into the groove. Most tires also have built-in wear indicators (TWI bars) at 1.6 mm.

Why does the calculator show different limits for winter tires?

Winter tires rely on deep sipes (thin cuts in the tread blocks) for snow and ice grip. Below 4 mm, the sipes are too shallow to channel snow and slush effectively. At 3 mm, a winter tire performs about the same as a summer tire in snow. That is why the recommended replacement depth is 4 mm for winter vs 3 mm for summer tires.

What causes uneven tire wear?

Two main causes. Edge wear (outer or inner side thinner than center) usually means incorrect wheel alignment (toe or camber) or chronic underinflation. Center wear (center thinner than edges) indicates overinflation. A difference of more than 1 mm across the tread face should be investigated. Fix the root cause before fitting new tires - otherwise the new set will wear the same way.

How many kilometers does 1 mm of tread last?

On average: summer tires wear about 6,500 km per mm, all-season about 5,500 km/mm, and winter tires about 5,000 km/mm (softer compound wears faster). These are averages - aggressive driving, poor alignment, and abrasive road surfaces can cut tire life by 30-50%. Highway driving at consistent speed extends tire life compared to city stop-and-go.

Should I replace tires based on age even if tread is fine?

Yes. Tire manufacturers recommend replacing tires older than 6 years regardless of tread depth. Rubber compounds degrade from UV exposure, ozone and temperature cycles, causing micro-cracks (dry rot) that weaken the tire structure. The DOT code on the sidewall shows the manufacturing date - for example, 2419 means week 24 of 2019. After 10 years, tires should not be used at all.

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Ready-made calculations

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