Inches to Metric Tire Calculator

Example Data Table

Formula Used

Width in millimeters: section width inches × 25.4

Sidewall height: (overall diameter − rim diameter) ÷ 2

Aspect ratio: (sidewall height mm ÷ section width mm) × 100

Circumference: overall diameter × π

Revolutions per mile: 63,360 ÷ circumference inches

How To Use This Calculator

1. Enter the tire diameter from the inch tire label.
2. Enter the tire section width in inches.
3. Enter the wheel rim diameter in inches.
4. Select a metric prefix and rounding style.
5. Add your current metric tire size for comparison.
6. Press the calculate button to view the result.
7. Use CSV or PDF buttons to save the output.

Inches To Metric Tire Conversion Guide

Why Tire Conversion Matters

Inch tire labels are common on trucks, off-road builds, trailers, and older fitment charts. Metric labels are common on modern passenger tires. This calculator connects both systems. It helps you compare tires before buying them. It also helps you avoid guesswork.

Reading Inch Tire Sizes

A size like 33x12.50R15 has three main values. The first number is overall diameter. The second number is section width. The final number is wheel diameter. All three values are measured in inches. The R means radial construction.

Reading Metric Tire Sizes

A metric size like LT285/70R17 uses another format. The first number is width in millimeters. The second number is sidewall height as a percentage of width. The final number is rim diameter. Rim size still uses inches. That detail often surprises new users.

Fitment Planning

A close metric match may not be perfect. Tire makers use design tolerances. Actual diameter can vary by brand, tread pattern, load rating, and pressure. Wheel width also changes the mounted shape. Always compare manufacturer specifications when clearance is tight.

Speed And Clearance

Larger tires travel farther per wheel rotation. Your speedometer may read low. Smaller tires can make it read high. The comparison fields estimate this change. They also estimate ride height difference. Half the diameter change affects ground clearance.

Best Use

Use this tool for planning, shopping, and quick fitment checks. It is helpful for custom wheels and tire swaps. It is not a replacement for a professional fitment inspection. Check brake clearance, suspension travel, fender space, load index, and speed rating before installation.

FAQs

1. What does an inch tire size mean?

It shows overall diameter, section width, and rim diameter. A size like 33x12.50R15 means 33 inches tall, 12.50 inches wide, and a 15 inch rim.

2. Is the metric result always exact?

No. It is a calculated match. Real tire dimensions vary by brand, tread design, load range, pressure, and measuring method.

3. Why is rim size still shown in inches?

Metric tire labels use millimeters for width and percent for sidewall ratio. Rim diameter remains listed in inches across common tire sizing systems.

4. What is aspect ratio?

Aspect ratio is sidewall height as a percentage of tire width. A 70 aspect tire has a sidewall height equal to 70 percent of its width.

5. Can this calculator compare speedometer change?

Yes. Enter your current metric tire size. The calculator compares diameters and estimates the actual speed at your chosen indicated speed.

6. What diameter change is acceptable?

Many planners try to stay within three percent. Larger changes may affect gearing, braking, clearance, stability systems, and speedometer accuracy.

7. Does this check load rating?

No. It converts size values and estimates fitment numbers. Always verify load index, speed rating, tire type, and vehicle requirements separately.

8. Can I use it for off-road tires?

Yes. It is useful for off-road inch sizes. Still check real manufacturer measurements, because aggressive tread designs often measure differently.