Tire Size Calculator And Comparison
A tire size such as 265/70R17 gives nominal width, aspect ratio and rim diameter. Estimated outside diameter combines the rim and two sidewall heights.
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NIST describes the standard inch as exactly equivalent to 25.4 mm
. NIST length definition. Michelin — reading tire markings. Method and limitations.
Calculate complete tire dimensions with automatic mm to inches conversion. Compare tire sizes, understand measurements, and estimate geometry before checking manufacturer fitment, clearance, rim width, load and speed requirements.
Tire Size Calculator
How To Read Tire Size
Example: 265/70R17
- • 265 = Section width in millimeters
- • 70 = Aspect ratio (sidewall height as % of width)
- • R = Radial construction
- • 17 = Wheel diameter in inches
Tire Size Comparison
Enter sizes in either metric format (e.g., 205/55R16) or floating imperial format (e.g., 31x10.5R15). We calculate diameter, sidewall, circumference, revs/mile, and key differences.
A: 205/55R16
B: 225/45R17
Tire Size Chart
A practical tire size chart showing inches and millimeters. Toggle by rim size or overall tire diameter, curated from common passenger car, SUV and pickup fitments.
Rim 15"
| Tire Size | Overall Diameter | Section Width | Wheel/Rim |
|---|---|---|---|
| 185/65R15 | 24.47" (622mm) | 7.28" (185mm) | 15" (381mm) |
| 195/60R15 | 24.21" (615mm) | 7.68" (195mm) | 15" (381mm) |
| 195/65R15 | 24.98" (635mm) | 7.68" (195mm) | 15" (381mm) |
| 205/65R15 | 25.49" (648mm) | 8.07" (205mm) | 15" (381mm) |
| 215/70R15 | 26.85" (682mm) | 8.46" (215mm) | 15" (381mm) |
| 235/75R15 | 28.88" (734mm) | 9.25" (235mm) | 15" (381mm) |
| 31x10.5R15 | 31.00" (787mm) | 10.50" (267mm) | 15" (381mm) |
Rim 16"
| Tire Size | Overall Diameter | Section Width | Wheel/Rim |
|---|---|---|---|
| 205/55R16 | 24.88" (632mm) | 8.07" (205mm) | 16" (406mm) |
| 205/60R16 | 25.69" (652mm) | 8.07" (205mm) | 16" (406mm) |
| 215/55R16 | 25.31" (643mm) | 8.46" (215mm) | 16" (406mm) |
| 215/60R16 | 26.16" (664mm) | 8.46" (215mm) | 16" (406mm) |
| 225/60R16 | 26.63" (676mm) | 8.86" (225mm) | 16" (406mm) |
| 225/70R16 | 28.40" (721mm) | 8.86" (225mm) | 16" (406mm) |
| 245/75R16 | 30.47" (774mm) | 9.65" (245mm) | 16" (406mm) |
| 265/75R16 | 31.65" (804mm) | 10.43" (265mm) | 16" (406mm) |
| 285/75R16 | 32.83" (834mm) | 11.22" (285mm) | 16" (406mm) |
Rim 17"
| Tire Size | Overall Diameter | Section Width | Wheel/Rim |
|---|---|---|---|
| 215/55R17 | 26.31" (668mm) | 8.46" (215mm) | 17" (432mm) |
| 225/50R17 | 25.86" (657mm) | 8.86" (225mm) | 17" (432mm) |
| 225/55R17 | 26.74" (679mm) | 8.86" (225mm) | 17" (432mm) |
| 225/65R17 | 28.52" (724mm) | 8.86" (225mm) | 17" (432mm) |
| 235/50R17 | 26.25" (667mm) | 9.25" (235mm) | 17" (432mm) |
| 235/55R17 | 27.18" (690mm) | 9.25" (235mm) | 17" (432mm) |
| 265/70R17 | 31.61" (803mm) | 10.43" (265mm) | 17" (432mm) |
| 285/70R17 | 32.71" (831mm) | 11.22" (285mm) | 17" (432mm) |
| 33x12.5R17 | 33.00" (838mm) | 12.50" (318mm) | 17" (432mm) |
Rim 18"
| Tire Size | Overall Diameter | Section Width | Wheel/Rim |
|---|---|---|---|
| 235/45R18 | 26.33" (669mm) | 9.25" (235mm) | 18" (457mm) |
| 235/50R18 | 27.25" (692mm) | 9.25" (235mm) | 18" (457mm) |
| 245/45R18 | 26.68" (678mm) | 9.65" (245mm) | 18" (457mm) |
| 255/55R18 | 29.04" (738mm) | 10.04" (255mm) | 18" (457mm) |
| 275/65R18 | 32.07" (815mm) | 10.83" (275mm) | 18" (457mm) |
| 275/70R18 | 33.16" (842mm) | 10.83" (275mm) | 18" (457mm) |
Rim 19"
| Tire Size | Overall Diameter | Section Width | Wheel/Rim |
|---|---|---|---|
| 235/40R19 | 26.40" (671mm) | 9.25" (235mm) | 19" (483mm) |
| 245/40R19 | 26.72" (679mm) | 9.65" (245mm) | 19" (483mm) |
| 245/45R19 | 27.68" (703mm) | 9.65" (245mm) | 19" (483mm) |
| 255/40R19 | 27.03" (687mm) | 10.04" (255mm) | 19" (483mm) |
Rim 20"
| Tire Size | Overall Diameter | Section Width | Wheel/Rim |
|---|---|---|---|
| 255/45R20 | 29.04" (738mm) | 10.04" (255mm) | 20" (508mm) |
| 265/50R20 | 30.43" (773mm) | 10.43" (265mm) | 20" (508mm) |
| 275/55R20 | 31.91" (811mm) | 10.83" (275mm) | 20" (508mm) |
| 275/60R20 | 32.99" (838mm) | 10.83" (275mm) | 20" (508mm) |
| 285/50R20 | 31.22" (793mm) | 11.22" (285mm) | 20" (508mm) |
| 35x12.5R20 | 35.00" (889mm) | 12.50" (318mm) | 20" (508mm) |
Common Tire Width Conversions
| Example Tire Size | Width (mm) | Width (inches) |
|---|---|---|
| 205/55R16 | 205mm | 8.07" |
| 215/60R16 | 215mm | 8.46" |
| 225/65R17 | 225mm | 8.86" |
| 235/55R18 | 235mm | 9.25" |
| 245/45R19 | 245mm | 9.65" |
| 255/50R20 | 255mm | 10.04" |
| 265/70R17 | 265mm | 10.43" |
| 275/55R20 | 275mm | 10.83" |
How To Read Tire Size
A typical tire size like 205/55R16 contains several measurements:
- 205 - Section width in millimeters (8.07 inches)
- 55 - Aspect ratio (sidewall height as % of width)
- R - Radial construction
- 16 - Wheel diameter in inches
The first number (section width) is always in millimeters, which is why understanding mm to inches conversion is crucial for tire selection and comparison.
Frequently Asked Questions
The first number in a tire size (e.g., 205 in 205/55R16) represents the tire's section width in millimeters, measured from sidewall to sidewall. To convert this to inches, divide by 25.4 (e.g., 205mm ÷ 25.4 = 8.07 inches).
Tire width is always given in millimeters. To convert to inches, use the formula: inches = mm ÷ 25.4. For example, a 225mm tire is 225 ÷ 25.4 = 8.86 inches wide. Our mm to inches converter performs this calculation accurately and instantly.
The aspect ratio (second number in tire size, e.g., 55 in 205/55R16) is a percentage of the section width. A 55 aspect ratio on a 205mm tire means the sidewall height is 205mm × 0.55 = 112.75mm (4.44 inches).
Not necessarily. Tire sizes are standardized globally using metric measurements (mm). However, understanding the inch equivalents can help you compare with older imperial tire sizes or understand your tire's actual dimensions in inches for clearance calculations.
Use tire sizes approved for your vehicle and rim. A small width difference alone does not establish compatibility; check clearance, load and speed ratings, axle requirements and manufacturer guidance with a qualified tire professional.
Compute rolling diameter for each size, then evaluate diameter delta %, speedometer error (real speed = indicated × candidate/oe), and approximate clearance change (delta/2). A small diameter difference is not a fitment approval; confirm the vehicle and tire manufacturer requirements.
Speedometer error arises from rolling diameter change. Real speed ≈ indicated speed × (new diameter ÷ old diameter). Larger diameter → higher real speed than indicated.
Yes. Parse overall diameter × width (R wheel-inch). Sidewall height = (overall diameter − wheel diameter) ÷ 2; width(mm) = width(in) × 25.4; compute unified metrics to compare.
Related Conversion Tools
Sources and calculation notes
A tire size such as 265/70R17 gives nominal width, aspect ratio and rim diameter. Estimated outside diameter combines the rim and two sidewall heights.
Method: Sidewall height in mm = width × aspect ratio / 100. Estimated diameter in mm = rim inches × 25.4 + 2 × sidewall height; circumference = π × diameter.
Scope: Actual inflated size and rolling circumference vary by product, load, pressure and wear. Fitment also requires clearance, rim width, load and speed checks.
Content maintained by mmtoinches.im. Updated and reference notes reviewed . How we calculate and present measurements. Sources support the stated definitions; examples and calculators are not certification of a product or compliance with a standard.