Metric Tire Size Decoder
Decode any metric tire size such as 225/45 R17 94W. See width, aspect ratio, construction, rim, load index and speed rating explained.
Explain width, aspect ratio, and rim diameter.
Metric Tire Size Decoder: Tire Size Inputs
Compare two tire sizes here. Use the formulas and reference tables below for this tool's specific calculation.
How Metric Tire Size Decoder Works?
The Metric Tire Size Decoder works by splitting the sidewall code into its fields and translating each field into a dimension or rating. The decoder reads 5 fields.
Read the prefix
The decoder identifies P (passenger), LT (light truck), ST (trailer), T (temporary) or no prefix (European metric).
Read the 3 size numbers
The decoder translates 225 into a 225 mm (8.86 in) width, 45 into a 45% aspect ratio and 17 into a 17 in (431.8 mm) rim.
Read the construction letter
The decoder translates R as radial, D as diagonal and B as belted bias.
Read the service description
The decoder translates 94W into a 670 kg (1,477 lb) load capacity and a 270 km/h (168 mph) speed rating.
Metric Tire Size Decoder Formula
The Metric Tire Size Decoder formula set turns the code W/AR R Rim LI SR into 3 dimensions: width W, sidewall W × AR ÷ 100 and diameter 2 × SH + Rim × 25.4.
[Prefix] W / AR [Construction] Rim [LI][SR] [XL]W_in = W ÷ 25.4SH = W × AR ÷ 100OD = 2 × SH + Rim × 25.4- W
- Section width (mm)
- AR
- Aspect ratio (%)
- LI
- Load index number
- SR
- Speed rating letter
Worked example
The code 235/45 R18 98Y XL decodes to a 235 mm (9.25 in) wide radial tire with a 105.75 mm (4.16 in) sidewall for an 18 in wheel, rated for 750 kg (1,653 lb) at up to 300 km/h (186 mph), with extra load construction. The overall diameter is 668.7 mm (26.33 in).
Metric Tire Size Decoder Conversion Table
The Metric Tire Size Decoder conversion table explains 13 fields that appear in metric tire codes.
| Field | Meaning | Example code |
|---|---|---|
| P | Passenger car (P-metric) | P225/45R17 |
| LT | Light truck | LT265/70R17 |
| ST | Special trailer | ST205/75R15 |
| T | Temporary spare | T125/70R16 |
| 225 | Section width 225 mm (8.86 in) | 225/45R17 |
| 45 | Aspect ratio 45% (sidewall 101.25 mm) | 225/45R17 |
| R | Radial construction | 225/45R17 |
| ZR | Radial rated above 240 km/h (149 mph) | 245/40ZR18 |
| D / B | Diagonal (bias) / belted bias | 6.00-16 |
| 17 | Rim diameter 17 in (431.8 mm) | 225/45R17 |
| 94 | Load index 94 = 670 kg (1,477 lb) | 225/45R17 94W |
| W | Speed rating 270 km/h (168 mph) | 225/45R17 94W |
| XL | Extra load construction | 225/45R17 94W XL |
What is Metric Tire Size Decoder?
A Metric Tire Size Decoder is a tool that explains each part of a metric tire size marking in plain units. Metric sizing is the format on more than 90% of passenger car tires sold worldwide.
The metric format mixes units. Width is in millimeters, aspect ratio is a percentage, and rim diameter is in inches. The decoder converts all 3 into a single unit system.
P-metric and Euro-metric tires of the same size have slightly different load tables. A P225/45R17 and a 225/45R17 tire share dimensions but not always load capacity.
What are the uses of Metric Tire Size Decoder?
There are 4 main uses of the Metric Tire Size Decoder, including first-time tire buying and spec verification.
First-time tire buying
Read the existing tire before ordering replacements.
Spec verification
Confirm a quoted tire matches the door placard size and rating.
Used tire checks
Decode a used tire's size and service description before purchase.
Training
Teach new tire shop staff the meaning of each code field.
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