Tire Size Converter: Metric to Inches & Standard

Metric to Standard Tire Conversion Calculator

Convert between metric and standard tire sizes instantly with precise calculations for diameter, width, and sidewall height

Metric to Standard Converter

Typically ranges from 155 to 365 mm

Sidewall height as percentage of width

Standard to Metric Converter

Total tire height in inches

Tire section width in inches

Popular Tire Size Conversions

Click any size below for instant conversion results

315/75R16
≈ 34.6 x 12.4
285/75R16
≈ 32.8 x 11.2
265/70R17
≈ 31.6 x 10.4
285/70R17
≈ 32.7 x 11.2
305/70R16
≈ 32.8 x 12.0
33×12.50R17
≈ 315/70R17
35×12.50R20
≈ 325/60R20
37×13.50R20
≈ 355/55R20

How Tire Size Conversion Works

Metric to Standard Formula

Metric tire format: WIDTH/ASPECT RATIO R RIM DIAMETER

Example: 315/75R16

Sidewall Height = (Width in mm × Aspect Ratio) / 100 Overall Diameter = (2 × Sidewall Height / 25.4) + Rim Diameter Section Width = Width in mm / 25.4

Result: Diameter x Width R Rim (e.g., 34.6 x 12.4 R16)

Standard to Metric Formula

Standard tire format: DIAMETER x WIDTH R RIM DIAMETER

Example: 35×12.50R17

Sidewall Height = (Overall Diameter – Rim Diameter) / 2 Width in mm = Section Width × 25.4 Aspect Ratio = (Sidewall Height / Width in mm) × 100

Result: Width/Aspect R Rim (e.g., 315/70R17)

Conversion Examples Step-by-Step

Example 1: Converting 315/75R16 to Standard

Step 1: Calculate sidewall height
Sidewall = (315 mm × 75%) ÷ 100 = 236.25 mm

Step 2: Convert sidewall to inches
Sidewall = 236.25 ÷ 25.4 = 9.3 inches

Step 3: Calculate overall diameter
Diameter = (2 × 9.3) + 16 = 34.6 inches

Step 4: Convert width to inches
Width = 315 ÷ 25.4 = 12.4 inches

Result: 34.6 x 12.4 R16

Example 2: Converting 33×12.50R17 to Metric

Step 1: Calculate sidewall height
Sidewall = (33 – 17) ÷ 2 = 8 inches

Step 2: Convert width to millimeters
Width = 12.50 × 25.4 = 317.5 mm (round to 315 mm)

Step 3: Calculate aspect ratio
Aspect = (8 × 25.4) ÷ 315 × 100 = 64.5% (round to 65%)

Result: 315/65R17

Comprehensive Conversion Chart

Metric Size Standard Size Overall Diameter Section Width Sidewall Height
265/70R17 31.6 x 10.4 R17 31.6″ 10.4″ 7.3″
265/75R16 31.6 x 10.4 R16 31.6″ 10.4″ 7.8″
285/70R17 32.7 x 11.2 R17 32.7″ 11.2″ 7.9″
285/75R16 32.8 x 11.2 R16 32.8″ 11.2″ 8.4″
305/70R16 32.8 x 12.0 R16 32.8″ 12.0″ 8.4″
315/70R17 34.4 x 12.4 R17 34.4″ 12.4″ 8.7″
315/75R16 34.6 x 12.4 R16 34.6″ 12.4″ 9.3″
325/60R20 35.4 x 12.8 R20 35.4″ 12.8″ 7.7″
33×10.50R15 265/75R15 33.0″ 10.5″ 9.0″
33×12.50R17 315/70R17 33.0″ 12.5″ 8.0″
35×12.50R17 315/70R17 35.0″ 12.5″ 9.0″
35×12.50R20 325/60R20 35.0″ 12.5″ 7.5″
37×12.50R17 315/75R17 37.0″ 12.5″ 10.0″
37×13.50R20 355/55R20 37.0″ 13.5″ 8.5″

Tire Size Component Explained

Tire Width

The first number in metric tires (measured in millimeters) or second number in standard tires (measured in inches). Represents the tire’s cross-sectional width.

Aspect Ratio

The second number in metric sizes (percentage). Represents the sidewall height as a percentage of the tire width. Lower numbers mean shorter sidewalls.

Rim Diameter

The diameter of the wheel (measured in inches) that the tire is designed to fit. Must match your wheel size exactly for proper fitment.

Overall Diameter

The total height of the tire from ground to top. Critical for speedometer accuracy, gear ratios, and vehicle clearance calculations.

Sidewall Height

The distance from the rim to the tire tread. Calculated differently for metric (width × aspect ratio) vs standard ((diameter – rim) ÷ 2) formats.

Section Width

The measurement from sidewall to sidewall at the widest point of the tire. Affects handling, traction, and vehicle stance.

When to Convert Tire Sizes

Off-Road Vehicle Modifications

When upgrading to larger tires for better ground clearance, you’ll need to convert between formats to find equivalent sizes. For example, a popular 35-inch tire in standard format might be 315/70R17 in metric.

Tire Replacement Shopping

Some tire manufacturers primarily use metric sizing while others use standard sizing. Converting between formats helps you find the best prices and availability across brands.

Speedometer Calibration

Changing tire sizes affects speedometer accuracy. Converting sizes helps calculate the percentage difference in overall diameter to recalibrate your speedometer correctly.

Vehicle Clearance Planning

Before installing larger tires, convert sizes to determine exact overall diameter increases to avoid rubbing against fenders, suspension components, or the frame.

Frequently Asked Questions

What is the difference between metric and standard tire sizes?
Metric tire sizes (like 315/75R16) use millimeters for width and a percentage for aspect ratio, while standard sizes (like 35×12.50R16) use inches for both overall diameter and width. Metric sizing provides more precision, while standard sizing is more intuitive for visualizing tire dimensions.
Can I replace metric tires with standard tires?
Yes, as long as the converted dimensions are similar. The overall diameter should be within 3% of the original tire size to avoid speedometer errors and clearance issues. Always verify that the rim diameter matches and check load ratings.
How accurate are tire size conversions?
Conversions provide close approximations, but actual tire dimensions can vary slightly between manufacturers. Tire widths are rounded to standard sizes (typically in 10mm increments for metric), and aspect ratios are rounded to the nearest 5%. Always verify final dimensions with manufacturer specifications.
What does the aspect ratio number mean?
The aspect ratio is the second number in metric tire sizes (the 75 in 315/75R16). It represents the sidewall height as a percentage of the tire width. A 75 aspect ratio means the sidewall height is 75% of the tire’s width. Lower aspect ratios create shorter, stiffer sidewalls for better handling.
Why do some conversions show multiple possible sizes?
Because metric sizes use specific increments (width in 10mm steps, aspect ratios in 5% steps), there isn’t always an exact metric equivalent for a standard size. Multiple metric sizes may have similar overall diameters, so choose based on your width preference and vehicle compatibility.
Will changing tire size affect my speedometer?
Yes. Your speedometer is calibrated for a specific tire diameter. If you install tires with a larger overall diameter, your speedometer will read slower than your actual speed. A 3% increase in diameter results in roughly 3% speedometer error. Many vehicles can be recalibrated electronically.
What is the R in tire sizes?
The “R” stands for Radial construction, which is the standard tire construction method today where tire cords run radially from bead to bead. Nearly all modern tires are radial. Some older tires may show “B” for bias-ply or “D” for diagonal construction.
How do I know which tire size fits my vehicle?
Check your vehicle’s door jamb sticker, owner’s manual, or the sidewall of your current tires for the recommended size. When upgrading, ensure the new size maintains similar overall diameter and doesn’t exceed your vehicle’s clearance limits or load capacity requirements.

Additional Tire Measurements

Tire Circumference

Calculate as π × overall diameter. Important for accurate odometer readings and determining how far your vehicle travels per wheel rotation.

Revolutions Per Mile

Calculated as 63,360 ÷ (π × diameter). Shows how many times the tire rotates in one mile, affecting gear ratios and fuel efficiency.

Load Index Rating

A numerical code indicating maximum weight capacity per tire. Must meet or exceed your vehicle’s requirements, especially when hauling or towing.

Speed Rating

A letter code (like H, V, or W) indicating maximum safe sustained speed. Higher performance vehicles require higher speed ratings.

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