Tire size conversion calculator

Use the calculator bellow to convert tire size from metric to inches or inches to metric:

1. Intended Use

   The first part of the tire code consists of one or two letters (P, LT, ST, T) that indicate the type of vehicle the tire is designed for. Here's a quick rundown:

   • P (Passenger Car): These tires are meant for cars, SUVs, crossovers, minivans, and smaller pickup trucks. They offer a comfortable ride and are optimized for everyday driving.
   • LT (Light Truck): Designed for heavier loads and towing, LT tires are suitable for larger trucks and vehicles that need to haul or tow.
   • ST (Special Trailer): These tires are used for trailers, including boat trailers, utility trailers, and travel trailers. They are built to handle the specific demands of towing.
   • T (Temporary): Usually spare tires, these are not intended for regular use. They are designed to get you to a service station in the event of a flat.

2. Nominal Section Width

   The second part of the code is a three-digit number representing the tire's nominal section width in millimeters (mm). This is the widest point of the tire, measured from sidewall to sidewall. For example, in a tire code "215/65R16", the "215" indicates the tire is 215 mm wide.

3. Aspect Ratio

   Following the nominal section width is the aspect ratio, displayed as a two- or three-digit number after a forward slash (/). This ratio compares the tire's section height to its width. A tire marked "215/65R16" has an aspect ratio of 65, meaning the height is 65% of the tire's width. For instance, if the width is 200 mm, an aspect ratio of 65 means the section height is 130 mm.

4. Internal Construction

   The next part of the code indicates the tire's internal construction with a single letter (R, D, B). This detail is crucial for understanding the tire's strength and durability:

   • R (Radial): Almost all passenger cars use radial tires, where the cords run perpendicular to the direction of travel. Radial construction provides flexibility and a smoother ride.
   • D (Diagonal): In diagonal or bias-ply tires, cords run at a 30-40° angle, crisscrossing over each other. These are less common in passenger vehicles but used in some trucks and specialty applications.
   • B (Bias-Belted): Similar to diagonal tires but with additional stabilizer belts. This construction provides extra support and stiffness, improving load capacity and durability.

5. Diameter of the Wheel

   The diameter of the wheel is specified next, usually as a one- or two-digit number indicating the size of the wheel in inches. In our example "215/65R16", the "16" signifies that the tire fits a 16-inch wheel. Ensuring the correct wheel diameter is vital for proper tire fit and vehicle performance.

6. Load Index

   The load index is a two- or three-digit number that tells you the maximum weight the tire can support when properly inflated. For instance, a load index of 95 means the tire can carry up to 1,520 pounds (690 kg) at a specified pressure. This information helps ensure your tires can handle the weight of your vehicle and any additional load.

   Load-Carrying Capacity Index
   Load index	Load in pounds (lbs)	Load in kilograms (kg)

   0	99	44.91
   1	102	46.27
   2	105	47.63
   3	107	48.53
   4	110	49.9
   5	114	51.71
   6	117	53.07
   7	120	54.43
   8	123	55.79
   9	128	58.06
   10	132	59.87
   11	136	61.69
   12	139	63.05
   13	143	64.86
   14	148	67.13
   15	152	68.95
   16	157	71.21
   17	161	73.03
   18	165	74.84
   19	171	77.56
   20	176	79.83
   21	182	82.55
   22	187	84.82
   23	193	87.54
   24	198	89.81
   25	204	92.53
   26	209	94.8
   27	215	97.52
   28	220	99.79
   29	227	102.97
   30	234	106.14
   31	240	108.86
   32	247	112.04
   33	254	115.21
   34	260	117.93
   35	267	121.11
   36	276	125.19
   37	282	127.91
   38	291	132
   39	300	136.08
   40	309	140.16
   41	320	145.15
   42	331	150.14
   43	342	155.13
   44	353	160.12
   45	364	165.11
   46	375	170.1
   47	386	175.09
   48	397	180.08
   49	408	185.07
   50	419	190.06
   51	430	195.04
   52	441	200.03
   53	454	205.93
   54	467	211.83
   55	481	218.18
   56	494	224.07
   57	507	229.97
   58	520	235.87
   59	536	243.13
   60	551	249.93
   61	567	257.19
   62	584	264.9
   63	600	272.16
   64	617	279.87
   65	639	289.85
   66	639	289.85
   67	677	307.08
   68	694	314.79
   69	716	324.77
   70	739	335.2
   71	761	345.18
   72	783	355.16
   73	805	365.14
   74	827	375.12
   75	852	386.46
   76	882	400.07
   77	908	411.86
   78	937	425.02
   79	963	436.81
   80	992	449.96
   81	1019	462.21
   82	1047	474.91
   83	1074	487.16
   84	1102	499.86
   85	1135	514.83
   86	1168	529.8
   87	1201	544.76
   88	1235	560.19
   89	1279	580.14
   90	1323	600.1
   91	1356	615.07
   92	1389	630.04
   93	1433	650
   94	1477	669.96
   95	1521	689.91
   96	1565	709.87
   97	1609	729.83
   98	1653	749.79
   99	1709	775.19
   100	1764	800.14
   101	1819	825.08
   102	1874	850.03
   103	1929	874.98
   104	1984	899.93
   105	2039	924.87
   106	2094	949.82
   107	2149	974.77
   108	2205	1000.17
   109	2271	1030.11
   110	2337	1060.05
   111	2403	1089.98
   112	2469	1119.92
   113	2535	1149.86
   114	2601	1179.79
   115	2679	1215.17
   116	2756	1250.1
   117	2833	1285.03
   118	2910	1319.95
   119	2998	1359.87
   120	3086	1399.79
   121	3197	1450.13
   122	3307	1500.03
   123	3417	1549.93
   124	3527	1599.82
   125	3638	1650.17
   126	3748	1700.06
   127	3858	1749.96
   128	3968	1799.85
   129	4079	1850.2
   130	4189	1900.1
   131	4289	1945.46
   132	4409	1999.89
   133	4541	2059.76
   134	4674	2120.09
   135	4806	2179.96
   136	4938	2239.84
   137	5071	2300.17
   138	5203	2360.04
   139	5357	2429.89
   140	5512	2500.2
   141	5677	2575.04
   142	5842	2649.89
   143	6008	2725.18
   144	6173	2800.03
   145	6393	2899.82
   146	6614	3000.06
   147	6779	3074.9
   148	6844	3104.39
   149	7165	3249.99
   150	7385	3349.78

7. Speed Rating

   The speed rating is the final part of the main tire code, represented by a letter or a combination of a digit and a letter. This rating indicates the maximum speed the tire can safely sustain. For example, a tire with a speed rating of "H" can safely travel up to 130 mph (210 km/h). Matching your tire's speed rating to your driving habits and vehicle specifications is essential for safety and performance.

   Speed index chart
   Speed rating	Maximum speed km/h	Maximum speed mph

   A1	5	3
   A2	10	6
   A3	15	9
   A4	20	12
   A5	25	16
   A6	30	19
   A7	35	22
   A8	40	25
   B	50	31
   C	60	37
   D	65	40
   E	70	43
   F	80	50
   G	90	56
   J	100	62
   K	110	68
   L	120	75
   M	130	81
   N	140	87
   P	150	94
   Q	160	100
   R	170	106
   S	180	112
   T	190	118
   U	200	124
   H	210	130
   V	240	149
   Z	over 240	over 149
   W	270	168
   (W)	over 270	over 168
   Y	300	186
   (Y)	over 300	over 186

8. DOT Code

   In addition to the main tire code, U.S. tires also feature a DOT code, mandated by the Department of Transportation. This code provides details about the tire's manufacturer, production plant, batch, mold, and the date of production. The last four digits of the DOT code are especially important, indicating the week and year the tire was made (e.g., "1321" means the 13th week of 2021). Tires older than ten years should generally be replaced, regardless of their apparent condition, due to material aging. The NHTSA recommends replacing tires every six years for optimal safety.