Tire Wear Calculator
Find out how much usable life your tires have left. Enter the current tread depth to see whether you are getting close to the legal limit or to the depth where aquaplaning becomes a real risk
Tread Measurements
Tire Status
How to use this tool
- Choose Millimeters (mm) or 32nds of an inch for your tread gauge.
- Enter the original tread depth of a new tire (check the manufacturer's data if unsure).
- Enter the current depth measured in the main groove with a tread gauge.
- Read the usable life remaining and the safety status: Safe, Caution or Replace Immediately.
Worked example
A tire that started at 8 mm and now measures 3 mm has (3 − 1.6) ÷ (8 − 1.6) ≈ 22% of its usable life left, and the status is Caution, because 3 mm is the tool's planning threshold for wet-road grip. A tire at 6/32 inch that began at 10/32 shows 50% (the legal limit in this mode is 2/32). Measure in several places across the tread: uneven wear, a misaligned axle or wrong pressure can leave one edge much lower than the center.
Why this tool exists and where its numbers come from
Worn tread clears water worse, and many places set a legal minimum depth. The tool measures what is left between a new tire and the 1.6 mm limit used in the EU, the UK and Brazil; the 3 mm caution line is the tool's own threshold, not a legal figure.
Sources
- GOV.UK: The Highway Code, Annex 6 (tyres, minimum tread 1.6 mm)
- Council Directive 89/459/EEC (tread depth), legislation.gov.uk copy
- CONTRAN Resolução 913/2022 (Brasil), texto reproduzido
For the full method, see the Methodology section just below.
Methodology
This tool expresses tire wear as the share of usable tread left between a brand-new tire and the legal minimum: remaining life % = (current depth − limit) / (new depth − limit) × 100. The limit is 1.6 mm in millimeter mode and 2/32 inch in 32nds mode, and the result is capped between 0% and 100%. Example: a tire that started at 8 mm and now measures 6 mm has (6 − 1.6) / (8 − 1.6) = 69% of its usable life left; in 32nds, 10/32 new and 6/32 now gives (6 − 2) / (10 − 2) = 50%.
Tomás checks his front tire in three places
Tomás has a tire that started at 8 mm. With a depth gauge he measures the main groove at three points across the tread: inner shoulder 4.1 mm, center 5.2 mm, outer shoulder 6.0 mm.
- Entering the center reading (5.2 mm) gives (5.2 − 1.6) ÷ (8 − 1.6) = 56% usable life, status Safe. That is the flattering number.
- The outer shoulder (6.0 mm) gives 69%. Still comfortable.
- The inner shoulder (4.1 mm) gives (4.1 − 1.6) ÷ 6.4 = 39%, also Safe, and it is the one that counts, since the shallowest spot decides when the tire is done.
- Three months earlier that same spot read 5.0 mm, so it lost about 0.3 mm a month. By hand, at that pace it reaches the tool's 3 mm caution line in roughly four months and the 1.6 mm limit in roughly eight.
Tomás books a replacement and an alignment check before the four-month mark, because that much more wear on one shoulder points to alignment or pressure. A straight-line forecast is only a rough guide, and a tire professional should confirm the tire's condition.
Essential Automotive Gear
Tools for measuring tread and pressure and for keeping a tire inflated on the road
Digital Tire Tread Depth Gauge, 0–25.4 mm
A digital tread depth gauge measuring 0 to 25.4 mm with an LCD display, according to the listing.
AstroAI L7 Tire Inflator Portable Air Compressor
A cordless inflator rated to 150 PSI with auto shut-off and a digital display, according to the listing.
Blackjack KT-340 Tire Repair Kit
A tire plug kit for temporary puncture repairs, according to the listing. Have the tire checked by a tire shop afterwards.
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Frequently asked questions
How do I measure my tire's current tread depth? ▼
Use a tread depth gauge, or look for the small rubber bars (tread wear indicators) inside the grooves. If the tread is level with these bars, the tire has reached the 1.6 mm legal limit.
Why does the tool show a “Caution” warning before the legal limit? ▼
Because grip starts to suffer well before the legal limit. At around 3 mm of tread, a tire clears water much less effectively, so stopping distances on wet roads get noticeably longer.
Why does the percentage look lower than the tread I can see? ▼
The percentage measures usable life between a new tire and the legal limit, not total tread depth. For example, 4.8 mm on a tire that started at 8 mm and has a 1.6 mm limit shows about 50%. It also relies on a single reading, so uneven wear is not captured. Have a tire professional inspect your tires if in doubt.
How do millimeters and 32nds of an inch relate, and where should I measure? ▼
One 32nd of an inch is about 0.79 mm, so 2/32 is roughly 1.6 mm and 4/32 roughly 3.2 mm. The tool uses 3 mm as its caution line in millimeter mode and 4/32 in 32nds mode, so the two modes can differ by a fraction of a millimeter. Measure in the main grooves at several points across the width and around the circumference, because the inner or outer shoulder often wears faster than the center when alignment or pressure is off. Enter the lowest reading, since the shallowest spot decides when the tire is no longer fit for use.